Abstract

INTRODUCTION

Climatic conditions in the Cuban archipelago are determined by its geographical position close to the Tropic of Cancer, where it receives high levels of solar radiation throughout the year. The country’s long, narrow profile and maritime situation temper the behavior of the main climate variables. Cuba’s climate is tropical and seasonally humid, with semicontinental features due to its proximity to North America.[¹1. Planos GE, Rivero VR, Guevara VV, editors. Impacto del cambio climático y medidas de adaptación en Cuba. 1st ed. Havana: Editorial AMA; 2013. p. 401–30. Spanish.] It has two well-defined seasons: a summer rainy season (May–October), influenced by ocean weather systems; and a winter dry season (November–April), with greater influence by continental high pressure systems and cold fronts.

Weather (temperature, humidity, atmospheric pressure, precipitation conditions) and climate (long-term average weather conditions) can affect natural, human and socioeconomic systems, with consequences for human health.[²2. Ortíz Bultó PL, Rodriguez AP, Rivero Valencia A, León Vega N, Diaz González M, Pérez Carrera A. Assessment of human health vulnerability to climate variability and change in Cuba. Environ Health Perspect [Internet]. 2006 Dec 11 [cited 2013 Aug 17];114(12):1942–9. Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/pmid/17185289/
http://www.ncbi.nlm.nih.gov/pmc/articles... ] Local climate characteristics can affect population morbidity and mortality; e.g., the pronounced seasonal variation may account for an acute myocardial infarction (AMI) mortality rate higher in winter than in summer.[³3. Dilaveris P, Synetos A, Giannopoulos G, Gialafos E, Pantazis A, Stefanadis C. Climate impacts on myocardial infarction deaths in the Athens territory: the CLIMATE study. Heart. 2006 Dec;92(12):1747–51.,⁴4. Rivero VA. Clima y mortalidad por infarto agudo de miocardio en Cuba 2000–2005 [thesis]. [Havana]: University of Havana; 2008. Spanish.] Human capacity for adaptation and self-regulation through homeostasis enables us to adapt to diverse climates and environments, but we remain vulnerable to major shifts in extremes of meteorological and climatic conditions (hotter or colder, wetter or drier) or to abrupt climate changes that may exceed our physiological ability to adapt.[⁵5. Lecha Estela LB, de Carvajal EC, Estrada Moreno A, Gómez Acosta EC. Pronósticos biometeorológicos: via para reducir la ocurrencia de crisis de salud. Caso Sagua la Grande. Rev Cubana Salud Pública [Internet]. 2008 Jan–Mar [cited 2015 Mar 13];34(1). Available from: http://scielo.sld.cu/scielo.php?script=sci_arttext&pid=S0864-34662008000100009&lng=es&nrm=iso. Spanish.
http://scielo.sld.cu/scielo.php?script=s... ]

Current climate variability, instability and changes in atmospheric circulation patterns, such as El Niño and La Niña events, are having an impact on the environment with adverse effects on health, and potential consequences for life on Earth.[⁶6. Martens P, McMichael AJ, editors. Environmental change: climate and health. Issues and research methods. Cambridge: University of Cambridge; 2009 Sep. 366 p.,⁷7. Pan American Health Organization. Cambio climático y salud humana: riesgos y respuestas. Resumen actualizado 2008. Washington, D.C: World Health Organization; 2008. 40 p. Spanish.]

AMI is a health problem of global importance and one of the leading causes of morbidity and mortality.[⁸8. Goerre S, Egli C, Gerber S, Defila C, Minder C, Richner H, et al. Impact of weather and climate on the incidence of acute coronary syndromes. Int J Cardiol. 2007 May 16;118(1):36–40.,⁹9. Boersma E, Mercado N, Poldersman D, Gardien M, Vos J, Simoons ML. Acute myocardial infarction. Lancet. 2003 Mar 8;361(9360):847–58.] For several years now, AMI has been one of the leading causes of death in Cuba, with mortality rates ranging from 197.6 to 211.8/100,000 population from 2009 to 2012.[¹⁰10. National Health Statistics and Medical Records Division (CU). Anuario Estadistico de Salud 2010 [Internet]. Havana: Ministry of Public Health (CU); 2011 [cited 2014 Apr 14]. 174 p. Available from: http://files.sld.cu/dne/files/2011/04/anuario-2010-e-sin-graficos1.pdf. Spanish.
http://files.sld.cu/dne/files/2011/04/an... ,¹¹11. National Health Statistics and Medical Records Division (CU). Anuario Estadistico de Salud 2012 [Internet]. Havana: Ministry of Public Health (CU); 2013 Apr [cited 2014 Apr 14]. 190 p. Available from: http://files.sld.cu/dne/files/2013/04/anuario_2012.pdf. Spanish.
http://files.sld.cu/dne/files/2013/04/an... ] In Cuba, as in the rest of the world, AMI mortality is higher in urban settings, in provincial capitals, urban, and urban-rural municipalities.[¹²12. Kriszbacher I. Seasonal and diurnal variation in the occurrence of acute myocardial infarction and the effects of weather changes [thesis]. [Pécs]: University of Pécs; 2006 [cited 2014 Jul 17]. 17 p. Available from: http://doktoriiskola.etk.pte.hu/dok/doktoriiskola/disszertaciok/kriszbacher_te zisek_angol.pdf
http://doktoriiskola.etk.pte.hu/dok/dokt... ,¹³13. Arias Morales PL, Barrero Varón SL, Granada Romero J, Gallego González CA, Lazo Acosta AE, Monge Cardona IC, et al. Caracterización de los pacientes con infarto agudo de miocardio en un hospital de nivel 2. Arch Med (Colombia). 2006 Dec;(13):10–22. Spanish.] It is still not clear, however, how weather variations and climate change affect AMI mortality patterns, since other powerful determining factors make it difficult to detect smaller changes attributable to climate variability.[¹1. Planos GE, Rivero VR, Guevara VV, editors. Impacto del cambio climático y medidas de adaptación en Cuba. 1st ed. Havana: Editorial AMA; 2013. p. 401–30. Spanish.]

The seasonal rhythm of AMI mortality is well known.[³3. Dilaveris P, Synetos A, Giannopoulos G, Gialafos E, Pantazis A, Stefanadis C. Climate impacts on myocardial infarction deaths in the Athens territory: the CLIMATE study. Heart. 2006 Dec;92(12):1747–51.,⁴4. Rivero VA. Clima y mortalidad por infarto agudo de miocardio en Cuba 2000–2005 [thesis]. [Havana]: University of Havana; 2008. Spanish.,¹⁴14. Corvalan C. Cambios ambientales globales y salud. Geneva: World Health Organization; 2004. Spanish. 15. González Hernández E, Cabadés O’Callaghan A, Cebrián Doménech J, López Merino V, Sanjuán Manez R, Echánove Errazti I, et al. [Seasonal variations in admissions for acute myocardial infarction. The PRIMVAC Study]. Rev Esp Cardiol [Internet]. 2004 Jan [cited 2014 Jul 24];57(1):12–9. Available from: http://www.revespcardiol.org/en/variaciones-estacionales-los-ingresos-por/articulo/13056528/. Spanish.
http://www.revespcardiol.org/en/variacio... 16. Crawford VL, McCann M, Stout RW. Changes in seasonal deaths from myocardial infarction. QJM. 2003 Jan;96(1):45–52. 18. Loughnan ME, Nicholls N, Tapper NJ. Demographic seasonal and spatial differences in acute myocardial infarction admissions to hospital in Melbourne, Australia. Int J Health Geogr [Internet]. 2008 Jul 30 [cited 2014 Jul 24];7:42. Available from: http://www.ij-healthgeographics.com/content/7/1/42
http://www.ij-healthgeographics.com/cont... 19. Bhaskaran K, Hajat S, Haines A, Herrett E, Wilkinson P, Smeeth L. Short term effects of temperature on risk of myocardial infarction in England and Wales: time series regression analysis of the Myocardial Ischaemia National Audit Project (MINAP) registry. BMJ. 2010 Aug;341:c3823. DOI:10.1136/bmj.c3823.
10.1136/bmj.c3823... 23. Madrigano J, Murray A, Baccarelli A, Goldberg R, Melly S, von Klot S, et al. Temperature, myocardial infarction, and mortality: effect modification by individual and area-level characteristics. Epidemiology. 2013 May;24(3):439–46.–²¹21. Michelozzi P, De Sario M, Accetta G, de’Donato F, Kirchmayer U, Perucci CA, et al. Temperature and summer mortality: geographical and temporal variations in four Italian cities. J Epidemiol Community Health. 2006 May;60(5):417–23.] Prominent peaks occur in the coldest months of the year, and secondary peaks in the warmest months.[²²22. Stefanadis CI. Environment and the heart. Hellenic J Cardiol [Internet]. 2007 Sep–Oct [cited 2014 Jul 24];48:317–8. Available from: http://www.hellenicjcardiol.com/archive/full_text/2007/5/2007_5_317.pdf
http://www.hellenicjcardiol.com/archive/... –²⁴24. Arrastia AM, Limia MM. Energia y cambio climático. Havana: Editorial Academia; 2011. 247 p. Spanish.]

Cuba’s climate has changed in the last 40 years, bringing weather anomalies of varying intensities. The country has seen a 0.9 °C increase in mean annual temperature since 1951, a pronounced increase in minimum temperatures (of around 1.9 °C), a decrease in daily temperature range, and increased frequency and intensity of extreme events (drought, heavy rains, hurricanes, and both unusually cold and unusually hot months).[²⁵25. Montero Vega V, Montero Campello MJ, Sierra Figueredo P, Sierra Figueredo S, Frómeta Jiménez E. Mortalidad por infarto agudo de miocardio y su relación con las tormentas solares y geomagnéticas en la provincia Guantánamo. Rev Cubana Cardiol Cirugia Cardiovasc [Internet]. 2014 [cited 2015 Mar 20];20(2). Available from: http://www.revcardiologia.sld.cu/index.php/revcardiologia/article/view/516. Spanish.
http://www.revcardiologia.sld.cu/index.p... ] Projections estimate more extreme climatic conditions, with mean temperature increasing by as much as 4 °C, annual precipitation decreasing by >20% by the year 2050 and drought and extreme precipitation events increasing in frequency and intensity. Based on medium-range climate projections, warmer and wetter winters are expected, with large temperature and precipitation contrasts, along with warmer summers with greater temperature and humidity contrasts.[¹1. Planos GE, Rivero VR, Guevara VV, editors. Impacto del cambio climático y medidas de adaptación en Cuba. 1st ed. Havana: Editorial AMA; 2013. p. 401–30. Spanish.] These changes may in fact create favorable conditions for an increase in AMI mortality, with greater variability in the winter months.[²⁶26. Cámara DE. Variables meteorológicas y salud [Internet]. Madrid: Comunidad de Madrid. Publicaciones de Salud; 2006 Apr [cited 2015 Feb 12]. 113 p. Available from: http://www.madrid.org/cs/Satellite?c=CM_Publicaciones_FA&cid=1142292376363&language=es&pagename=Comunidad Madrid%2FEstructura. Spanish.
http://www.madrid.org/cs/Satellite?c=CM_... ]

There has been limited applied research on climatic impact on human health in Cuba. Temperature is one of the most-studied variables, but temperature does not act alone. At a given moment, the human body is exposed to a set of particular atmospheric conditions, a complex of meteorological variables (humidity, pressure, precipitation, etc.), with their effect depending on each individual’s relative susceptibility.[²⁶26. Cámara DE. Variables meteorológicas y salud [Internet]. Madrid: Comunidad de Madrid. Publicaciones de Salud; 2006 Apr [cited 2015 Feb 12]. 113 p. Available from: http://www.madrid.org/cs/Satellite?c=CM_Publicaciones_FA&cid=1142292376363&language=es&pagename=Comunidad Madrid%2FEstructura. Spanish.
http://www.madrid.org/cs/Satellite?c=CM_... ]

Since Havana has Cuba’s highest rates of AMI mortality;[¹⁰10. National Health Statistics and Medical Records Division (CU). Anuario Estadistico de Salud 2010 [Internet]. Havana: Ministry of Public Health (CU); 2011 [cited 2014 Apr 14]. 174 p. Available from: http://files.sld.cu/dne/files/2011/04/anuario-2010-e-sin-graficos1.pdf. Spanish.
http://files.sld.cu/dne/files/2011/04/an... ,¹¹11. National Health Statistics and Medical Records Division (CU). Anuario Estadistico de Salud 2012 [Internet]. Havana: Ministry of Public Health (CU); 2013 Apr [cited 2014 Apr 14]. 190 p. Available from: http://files.sld.cu/dne/files/2013/04/anuario_2012.pdf. Spanish.
http://files.sld.cu/dne/files/2013/04/an... ] it would be useful to know which predisposing climatic factors are involved, if any; which among them are most influential; and at what times of year they have a greater impact. Our objective in this study is to describe the relationship between climate variability and AMI mortality in Havana Province (known as Havana City Province until 2010) over the period 2001–2012.

METHODS

An ecological time-series study was conducted[²⁷27. Artiles Visbal L, Otero Iglesias J, Barrios Osuna I. Metodologia de la investigación para las ciencias de la salud. Havana: ECIMED; 2008. 355 p. Spanish.] of the universe of 23,744 AMI deaths in people of both sexes (I21–I22 in the ICD-10) having their official residence in Havana Province during the period January 2001–December 2012, inclusive. Data on cause of death were taken from medical death certificates. Individual characteristics for the studied variables of sex, date of death, place of residence, and underlying cause were taken from the National Medical Records and Health Statistics Bureau of the Ministry of Public Health. Population data were obtained from the National Statistics and Information Bureau.[²⁸28. National Statistics Bureau (CU) [Internet]. Havana: National Statistics Bureau (CU); c2015. Series Estadisticas 1985–2011; 2012 [cited 2014 Jul 28]. Available from: http://www.onei.cu/series2012.htm. Spanish.
http://www.onei.cu/series2012.htm... ] Number of deaths per month was used as a dependent variable to assess correlation with the Bultó-1 climatic index.[²2. Ortíz Bultó PL, Rodriguez AP, Rivero Valencia A, León Vega N, Diaz González M, Pérez Carrera A. Assessment of human health vulnerability to climate variability and change in Cuba. Environ Health Perspect [Internet]. 2006 Dec 11 [cited 2013 Aug 17];114(12):1942–9. Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/pmid/17185289/
http://www.ncbi.nlm.nih.gov/pmc/articles... ]

Study area

The study area comprised the current Havana Province, which is located between latitude 22°58′ N and 23°10′ N and between longitude 82°30′ W and 82°06′ W, and covers a land area of 726.75 km².[²⁹29. National Statistics Bureau (CU) [Internet]. Havana: National Statistics Bureau (CU); c2015. 2010: Una mirada a Cuba. La Habana; 2012 [cited 2014 Jul 28]; [about 1 screen]. Available from: http://www.onei.cu/publicaciones/provincias_masinf/la%20habana.htm. Spanish.
http://www.onei.cu/publicaciones/provinc... ] Its geographical boundaries are the Straits of Florida to the north, Mayabeque and Artemisa Provinces to the south, Mayabeque Province to the east, and Artemisa Province to the west.

From the database of the Climate Center at the Institute of Meteorology, climate data were obtained for the four weather stations considered by meteorologists to be representative of the study area, although not all are actually inside its borders: Casa Blanca, in Havana Province, representing the northern coast; Bauta, in Artemisa, representing the west end of Havana Province; Tapaste, in Mayabeque, representing the east; and Santiago de las Vegas, in Mayabeque, representing the south. Variables were mean maximum temperature, mean minimum temperature, mean relative humidity, atmospheric pressure, water vapor pressure, total precipitation, number of days with precipitation, and temperature range.

Data processing and analysis

The Bultó-1 index (which describes climate variations and trends, based on integration of the above-named climate variables) was used to describe climate variability for the study area.[²2. Ortíz Bultó PL, Rodriguez AP, Rivero Valencia A, León Vega N, Diaz González M, Pérez Carrera A. Assessment of human health vulnerability to climate variability and change in Cuba. Environ Health Perspect [Internet]. 2006 Dec 11 [cited 2013 Aug 17];114(12):1942–9. Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/pmid/17185289/
http://www.ncbi.nlm.nih.gov/pmc/articles... ] This index defines the signals of the basic seasonal climate variations that characterize Havana’s climate and their dynamics in space and time: the rainy season (warmer and wetter) when index values are positive, and the dry season (cooler and dryer) when values are negative. Factor analysis was used to determine which variables best explained climate characteristics and their association with AMI. Time-series analyses were used to determine the different signals of seasonal and interannual variation. Mann-Kendall and Pettitt statistical tests were used to characterize mortality trends.

To validate reporting of AMI as underlying cause of death, a thorough review of the data obtained was carried out to search for over-recording, to eliminate duplicate cases, and to include only residents in the selected area. An ACCESS database was created with reliable, high-quality information for the following fields: sex, date of death, place of residence, and underlying cause of death. Descriptive and inferential statistics were applied, using STATISTICA 7.0, EXCEL, and Winstat 2.0 software.

A time-series analysis was performed to determine the different signals of seasonal and interannual variation and to adjust time-series models with nonconstant variance for simulation of mortality patterns with STATISTICA 7.0. This application was also used to produce box-and-whisker plots for assessing the relationship between monthly AMI death rates and climate variability. Monthly mortality trends were analyzed using graphic output from the Winstat 2.0 program.

Factor analysis was used to study the interrelationships between the variables that make up the Bultó-1 index and AMI mortality, stipulating eigenvalues >1 and that the factors selected explain >70% of variance. To analyze the annual trend, the Winstat 2.0 program was used to run two nonparametric tests: Mann–Kendall and Pettitt,[³⁰30. Sneyers R. Sur l’analyse estatistique des series d’observations. Note Technique No. 143. OMM-No. 15. Geneva: World Meteorological Organization; 1975. p. 1–15. French.] the latter to identify possible structural changes in the series. A significance level of p ≤0.05 was used for both tests.

RESULTS

AMI mortality behavior and trends

In the period studied, a total of 23,744 AMI deaths were reported in Havana, for a mean annual rate of 91/100,000 population. Sex-specific rates were 104/100,000 in men and 79/100,000 in women.

A downward trend for deaths in men began in 2007, with a mortality rate of 109/100,000 population, reaching a low point of 80 in 2012. A less pronounced, but similar trend was seen for women, though with lower rates: in 2007 (80/100,000) and in 2012 (59/100,000).

Figure 1 shows the decrease in monthly deaths below the series mean starting in 2007, more pronounced starting in 2009.

Figure 2 displays the Pettitt test values, showing a statistically significant (p ≤0.05) downward trend in AMI mortality starting with a change point in April 2009. The results for the forward–backward Mann-Kendall were the same.

Seasonal AMI patterns

Mortality values were highest during the dry season that occurs during the Cuban winter months (November–April). The highest rates are in the months of January and December, the peak occurring in January, while the lowest mortality is found in the rainy season (May–October), with minimum values in the two-month April-May period (Figure 3). As inferred from factor analysis, pressure and temperature range were the most influential elements for the climate–AMI mortality relationship, with values other than 0 (process mean or breakeven point). The remaining variables were complemented with factor 2 (Figure 4).

AMI mortality response to climate variability

The response of AMI mortality to climate variability—expressed by the Bultó-1 index—is seen in the inverse relationship between index values and total AMI deaths. That is, when the index reached negative values below 1.5 in winter, AMI mortality increased, and when positive values were greater than 1.0 in summer, the number of deaths decreased. However, lower AMI deaths in summer were reported starting in 2011, with index values between 0 and somewhat higher than 0.5. This inverse association can explain the seasonal rhythm seen in AMI deaths (Figure 5).

In almost all cases, the highest AMI peaks occurred in January, except in 2007 and 2008, when they occurred in the months of November and December respectively. Mortality started to increase in November and December, reaching a peak in January. In April, deaths began a gradual decrease that continued until the months of July and August, when they reached secondary peaks, though not as pronounced as those in January.

DISCUSSION

Overall, a stable trend was seen from 2001 to 2006, and mortality rates began to decrease in 2007, influenced not only by climate variability anomalies (from winters that were warmer and less intense than usual, to feeling cold, even very cold) but also because of a reduction in acute phase mortality, due to a variety of factors, including earlier diagnosis of infarction, early and aggressive treatment, proper reperfusion treatment and more accurate delineation of postinfarction risk, along with more appropriate treatment of heart failure and post-infarction mechanical complications.[³¹31. Ferrer Castro JE, Fong Ocejo M, Rosell Castillo A, Guzmán Pérez N, Oliva Corujo L. Caracterización clínico epidemiológica de pacientes con infarto agudo de miocardio egresados de una unidad de cuidados intensivos. MEDISAN [Internet]. 2012 Aug [cited 2015 Mar 20]; 16(8): 1222–8. Available from: http://scielo.sld.cu/scielo.php?script=sci_arttext&pid=S1029 -30192012000800005&lng=es. Spanish.
http://scielo.sld.cu/scielo.php?script=s... ,³²32. Gutiérrez Loyola A, Druyet Castillo D, Oramas Domínguez I, Véliz Martínez PL. Infarto de miocardio en Cuba. Situación actual. Rev Cub Med Int Emerg [Internet]. 2010;9(1):1638–48. Available from: http://bvs.sld.cu/revistas/mie/vol9_1_10/mie04110.pdf. Spanish.
http://bvs.sld.cu/revistas/mie/vol9_1_10... ]

Concerning the statistically significant downward trend observed with the change point in the AMI mortality series starting in 2009, it could be supposed that in the last two years it has been oscillating around its mean. The trend pattern by year shows an increase from 2001 on, until the downward trend appeared in 2007, with slight variation in the last years. This might be associated, from a climate perspective, with significant weather and climate anomalies causing background bioclimatic conditions favorable to an increase in morbidity and mortality from many weather-sensitive diseases, including AMI. Of course, other factors or mechanisms linked to human behavior and not addressed in this study may have greater or lesser validity as a cause of mortality.

Influence exerted by the seasonal climate pattern, described by the Bultó-1 index, on AMI behavior was associated with greater mortality in dry-season months (November–April), peaking in January, characterized by colder and dryer climatic conditions with greater thermal contrasts and high pressure.[³3. Dilaveris P, Synetos A, Giannopoulos G, Gialafos E, Pantazis A, Stefanadis C. Climate impacts on myocardial infarction deaths in the Athens territory: the CLIMATE study. Heart. 2006 Dec;92(12):1747–51.,²⁶26. Cámara DE. Variables meteorológicas y salud [Internet]. Madrid: Comunidad de Madrid. Publicaciones de Salud; 2006 Apr [cited 2015 Feb 12]. 113 p. Available from: http://www.madrid.org/cs/Satellite?c=CM_Publicaciones_FA&cid=1142292376363&language=es&pagename=Comunidad Madrid%2FEstructura. Spanish.
http://www.madrid.org/cs/Satellite?c=CM_... ] In the rainy season (May–October), a relative maximum mortality was seen from June to August, under drier, extremely warm climate conditions, less contrasting or variable, with a relative increase in atmospheric pressure associated with strengthening of the oceanic anticyclone. In the transition months (April and November) between the two seasons, no notable changes were observed in mortality, which could be associated with the expansion of summer weather into the transitional periods.

Analysis of the monthly distribution of deaths showed that the highest concentration of annual mortality occurred during the dry season (November–April), which is wintertime in Cuba. Other studies are consistent with these findings, describing a seasonal variation in the increase in cardiac mortality associated with winter months in the United States, Europe, and Asia.[¹⁷17. Bhaskaran K, Hajat S, Haines A, Herrett E, Wilkinson P, Smeeth L. Effects of ambient temperature on the incidence of myocardial infarction. Heart. 2009 Nov;95(21):1760–9.,³³33. Xu B, Liu H, Su N, Kong G, Bao X, Li J, et al. Association between winter season and risk of death from cardiovascular diseases: a study in more than half a million inpatients in Beijing, China. BMC Cardiovasc Disord [Internet]. 2013 Oct 30 [cited 2015 Mar 20];13:93. Available from: http://www.biomedcentral.com/1471-2261/13/93
http://www.biomedcentral.com/1471-2261/1... 34. Barnett AG, Dobson AJ, McElduff P, Salomaa V, Kuulasmaa K, Sans S, et al. Cold periods and coronary events: an analysis of populations worldwide. J Epidemiol Community Health [Internet]. 2005 Jul [cited 2014 Jul 24];59(7):551–7. Available from: http://jech.bmj.com/content/59/7/551
http://jech.bmj.com/content/59/7/551... 35. McGregor GR. Winter North Atlantic oscillation, temperature and ischaemic heart disease mortality in three English counties. Int J Biometeorol. 2005 Jan;49(3):197–204. 37. Kendrovsky VT. The impact of temperature on mortality among the urban population in Skopje, Macedonia, during the period 1996–2000. BMC Public Health [Internet]. 2006 Feb 23 [cited 2014 Jul 24];6:44. Available from: http://www.biomedcentral.com/content/pdf/1471-2458-6-44.pdf
http://www.biomedcentral.com/content/pdf... –³⁹39. Olcina Cantos J, Martín Estévez D. Variaciones en la densidad del oxígeno en el aire y su influencia sobre la salud humana. Boletín Asoc Geógrafos Espanoles. 2012;(58):7–32. Spanish.] The increase in coronary event rates during cold periods is more pronounced in warmer than in colder climates.[³⁶36. Lee S, Lee E, Park MS, Kwon BY, Kim H, Jung DH, et al. Short-term effect of temperature on daily emergency visits for acute myocardial infarction with threshold temperatures. PLoS One [Internet]. 2014 Apr 25 [cited 2015 Mar 20];9(4):e94070. DOI :10.1371/journal.pone.0094070. Available from: http://www.plosone.org/article-info%3Adoi%2F10.1371%2Fjournal-pone.0094070#pone-0094070-g001
10.1371/journal.pone.0094070... ] Other associated contributors are higher oxygen pressure, wetter conditions, cooler conditions and precipitation different from the usual rainy season in either frequency or intensity.[⁴⁰40. Fernández de Arróyabe P. [Climate variability change as key concepts to develop biometeorological health warning systems] [Internet]. Santander: University of Cantabria; 2011 [cited 2013 Aug 17]. Available from: http://www.geobiomet.es. Spanish.
http://www.geobiomet.es... ]

The elements that compose the Bultó-1 index help to explain the relationship with AMI deaths. Pressure plays an important role. Low humidity also stands out as a predisposing parameter, particularly water vapor pressure. Dry air is infrequent in Cuba, occurring only with the arrival of dry and cold polar air masses, combined with extreme maximum and minimum temperatures. Conditions of high oxygen density increase AMI risk, affecting individuals differently according to their age, health status, lifestyle, and other environmental variables.[⁴⁰40. Fernández de Arróyabe P. [Climate variability change as key concepts to develop biometeorological health warning systems] [Internet]. Santander: University of Cantabria; 2011 [cited 2013 Aug 17]. Available from: http://www.geobiomet.es. Spanish.
http://www.geobiomet.es... ]

Lack of precipitation and high temperatures cause changes in body temperature, respiration, heart rate, and blood circulation, as the body’s metabolism and nervous system adapt. These changes can be severe and may contribute to increased AMI mortality.[²¹21. Michelozzi P, De Sario M, Accetta G, de’Donato F, Kirchmayer U, Perucci CA, et al. Temperature and summer mortality: geographical and temporal variations in four Italian cities. J Epidemiol Community Health. 2006 May;60(5):417–23.,³⁸38. Wichmann J, Rosengren A, Sjöberg A, Barregard L, Sallsten G. Association between ambient temperature and acute myocardial infarction hospitalizations in Gothenburg, Sweden: 1985–2010. PLoS One [Internet]. 2013 Apr 30 [cited 2015 Mar 20];8(4):e62059. DOI:10.1371/journal.pone.0062059. Available from: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0062059
10.1371/journal.pone.0062059... ,⁴⁰40. Fernández de Arróyabe P. [Climate variability change as key concepts to develop biometeorological health warning systems] [Internet]. Santander: University of Cantabria; 2011 [cited 2013 Aug 17]. Available from: http://www.geobiomet.es. Spanish.
http://www.geobiomet.es... ] When body temperature exceeds an upper threshold, thermolytic effector responses (sweating, increased peripheral blood flow) are activated and, when it falls below a lower base value, thermogenic responses (reduced peripheral blood flow, chills) are initiated. The consequences of these changes depend on their intensity and on individual resilience. In several of the years of the period under study, some months were among the hottest since 1951 and there were deficits in total accumulated rainfall.[⁴¹41. Institute of Meteorology (CU) [Internet]. Havana: Institute of Meteorology (CU); c1997–2015. Boletín de la Vigilancia del Clima. Centro del Clima. Características Climatológicas del Mes. Comportamiento de las temperaturas; 2012 Dec [cited 2013 Jan 20]; [about 1 screen]. Available from: http://www.insmet.cu/asp/genesis.asp?TB0=PLANTILLAS&TB1=ccCLIMA&TB2=/clima/CC/CCDiciembre2012.htm&TB3=2012. Spanish.
http://www.insmet.cu/asp/genesis.asp?TB0... –⁴⁴44. Institute of Meteorology (CU) [Internet]. Havana: Institute of Meteorology (CU); c1997–2015. Boletín de la Vigilancia del Clima. Centro del Clima. Características Climatológicas del Mes. Comportamiento de la temperatura; 2011 Dec [cited 2014 Jul 24]; [about 1 screen]. Available from: http://www.insmet.cu/asp/genesis.asp?TB0=PLANTILLAS&TB1=ccCLIMA&TB2=/clima/CC/CCDiciembre2011.htm&TB3=2011. Spanish.
http://www.insmet.cu/asp/genesis.asp?TB0... ]

The increase in AMI mortality during the early part of the study period could be associated with significant weather and climate anomalies that occurred in the Cuban archipelago, especially during winter months when it was largely subjected to the influence of El Niño–Southern Oscillation, and its counterpart, La Niña. These caused disturbances in weather and climate measurements that resulted in highly contrasting abnormal conditions, from persistence of very cold, dry days, particularly in January, to summers that were either very hot and humid or dry, with persistently high values in extreme temperatures (small temperature range).[⁴¹41. Institute of Meteorology (CU) [Internet]. Havana: Institute of Meteorology (CU); c1997–2015. Boletín de la Vigilancia del Clima. Centro del Clima. Características Climatológicas del Mes. Comportamiento de las temperaturas; 2012 Dec [cited 2013 Jan 20]; [about 1 screen]. Available from: http://www.insmet.cu/asp/genesis.asp?TB0=PLANTILLAS&TB1=ccCLIMA&TB2=/clima/CC/CCDiciembre2012.htm&TB3=2012. Spanish.
http://www.insmet.cu/asp/genesis.asp?TB0... ,⁴²42. Institute of Tropical Medicine (CU). Boletín Epidemiológico del IPK [Internet]. 2010 Dec [cited 2014 Jul 24];20(50). Available from: http://boletines.sld.cu/ipk/2010/12/18/vol-20-no-50-2010/. Spanish.
http://boletines.sld.cu/ipk/2010/12/18/v... ]

High ambient humidity hinders the body’s ability to cool off through sweat evaporation. In situations of intense heat when the body most needs this mechanism to release heat, sweat takes longer to evaporate, requiring more sweating. Small increases in temperature can seriously affect people. In Cuba, the mean annual temperature has risen by nearly 0.9 °C since 1951, and it is estimated that by 2100 it will have risen by between 2.7 °C and 7 °C. These temperature increases would contribute to an increase in AMI incidence.[²⁰20. OXFAM. Informe de investigación de OXFAM. El clima cambia, amenaza y exige adaptación: una mirada a la experiencia cubana de protección ante el cambio climático. United Kingdom: Oxfam Internacional; 2010 Oct. 37 p. Spanish.,²⁴24. Arrastia AM, Limia MM. Energia y cambio climático. Havana: Editorial Academia; 2011. 247 p. Spanish.]

With the more severe impact of a cold front (polar air mass) in winter, radiative exchange decreases, sweating stops, and cold stress on the body’s thermoregulatory system increases, the opposite of what happens in summer. In winters with extended periods of warmer temperatures, people maintain their adaptation to heat, and each blast by a cold front is felt more keenly. The most vulnerable population groups, the sick and elderly, have limited capacity to respond to persistent severe weather.[⁴4. Rivero VA. Clima y mortalidad por infarto agudo de miocardio en Cuba 2000–2005 [thesis]. [Havana]: University of Havana; 2008. Spanish.,³⁹39. Olcina Cantos J, Martín Estévez D. Variaciones en la densidad del oxígeno en el aire y su influencia sobre la salud humana. Boletín Asoc Geógrafos Espanoles. 2012;(58):7–32. Spanish.,⁴²42. Institute of Tropical Medicine (CU). Boletín Epidemiológico del IPK [Internet]. 2010 Dec [cited 2014 Jul 24];20(50). Available from: http://boletines.sld.cu/ipk/2010/12/18/vol-20-no-50-2010/. Spanish.
http://boletines.sld.cu/ipk/2010/12/18/v... ]

January 2001, the month with the highest AMI mortality, was the coldest since 1982 and one of the coldest since 1951, with strikingly low minimum temperatures (3.8°C).[⁴⁵45. Institute of Meteorology (CU)[Internet]. Havana: Institute of Meteorology (CU); c1997–2015. Boletín de la Vigilancia del Clima. Centro del Clima. Características Cli mato lógicas del Mes. Comportamiento de la temperatura; 2001 Dec [cited 2013 Jan 20]; [about 1 screen]. Available from: http://www.insmet.cu/asp/genesis.asp?TB0=PLANTILLAS&TB1=ccCLIMA&TB2=/clima/CC/CCDiciembre2001.htm&TB3=2001. Spanish.
http://www.insmet.cu/asp/genesis.asp?TB0... ] Something similar occurred in 2003 and 2010, when successive January cold fronts accentuated winter conditions, with persistently low minimum temperatures and little temperature variation.[⁴⁵45. Institute of Meteorology (CU)[Internet]. Havana: Institute of Meteorology (CU); c1997–2015. Boletín de la Vigilancia del Clima. Centro del Clima. Características Cli mato lógicas del Mes. Comportamiento de la temperatura; 2001 Dec [cited 2013 Jan 20]; [about 1 screen]. Available from: http://www.insmet.cu/asp/genesis.asp?TB0=PLANTILLAS&TB1=ccCLIMA&TB2=/clima/CC/CCDiciembre2001.htm&TB3=2001. Spanish.
http://www.insmet.cu/asp/genesis.asp?TB0... ] During the summer months in general, mean temperatures remained well above normal over the period, with high extreme temperatures and humidity.[⁴²42. Institute of Tropical Medicine (CU). Boletín Epidemiológico del IPK [Internet]. 2010 Dec [cited 2014 Jul 24];20(50). Available from: http://boletines.sld.cu/ipk/2010/12/18/vol-20-no-50-2010/. Spanish.
http://boletines.sld.cu/ipk/2010/12/18/v... ,⁴³43. Institute of Meteorology (CU) [Internet]. Havana: Institute of Meteorology (CU); c1997–2015. Boletín de la Vigilancia del Clima. Centro del Clima. Características Climatológicas del Mes. Comportamiento de la temperatura; 2010 Dec [cited 2014 Jul 24]; [about 1 screen]. Available from: http://www.insmet.cu/asp/genesis.asp?TB0=PLANTILLAS&TB1=ccCLIMA&TB2=/clima/CC/CCDiciembre2010.htm&TB3=2010. Spanish.
http://www.insmet.cu/asp/genesis.asp?TB0... ] The hot months were preceded and followed by extremely cold winter months. During transition periods, conditions were closer to normal. These assertions are consistent with other studies that also found physiological effects of climate, beyond the direct impacts of extreme climate events on health.[⁴⁶46. Ortíz PL, Pérez AR, Rivero VA, Perez AC, Ramón CJ, Lecha LE. La variabilidad y el cambio climático en Cuba: potenciales impactos en la salud humana. Rev Cubana Salud Pública [Internet]. 2008 Jan–Mar [cited 2013 Jan 20];34(1). Available from: http://scielo.sld.cu/scielo.php?pid=S0864-34662008000100008&script=sci_arttext. Spanish.
http://scielo.sld.cu/scielo.php?pid=S086... ]

This study had several limitations, including not having examined mortality in the age groups at greatest risk for AMI, and not having included such determinants as behavior, lifestyle, and prevalence of heart disease and hypertension (as well as other risk factors for cardiovascular disease by municipality). Furthermore, mortality as a dependent variable may be less susceptible to the impact of climate conditions than incidence, since access to and quality of health services can substantially affect survival.

This study is important, however, because only a few studies in Cuba and abroad have assessed the combined influence of a number of climatic factors on AMI; almost all studies to date have explored the impact of specific variables, such as rain and temperature. Another contribution made by this study is its demonstration of the applicability of the Bultó-1 index to studies of climate variability and change in relation to AMI mortality.

CONCLUSIONS

The Bultó-1 index is applicable to studies of climate variability and acute myocardial infarction mortality. Climate variability is inversely associated with an increase in acute myocardial infarction mortality. This inverse relationship helps explain the seasonal pattern of acute myocardial infarction mortality.

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