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pubmed:abstractText |
To determine whether skin surface cooling increases left ventricular preload and contractility to a greater extent in older compared with young adults we studied 11 young (28 +/- 2 yr; means +/- SE) and 11 older (64 +/- 3 yr) adults during normothermia (35 degrees C water perfused through a tube-lined suit) and cooling (15 degrees C water perfused for 20 min) using standard and tissue Doppler echocardiography. Cooling significantly decreased skin surface temperature in young (Delta2.8 +/- 0.3 degrees C) and older (Delta3.0 +/- 0.3 degrees C) adults and increased rate-pressure product, an index of myocardial oxygen demand, in older (6,932 +/- 445 to 7,622 +/- 499 mmHg x beats/min for normothermia and cooling, respectively), but not young (7,085 +/- 438 to 7,297 +/- 438 mmHg x beats/min) adults. Increases in blood pressure (systolic and mean blood pressure) during cooling were greater (P < 0.05) in older than in young adults. Cooling increased preload in older (left ventricular end-diastolic volume from 106 +/- 7 to 126 +/- 9 ml and left ventricular internal diameter in diastole from 4.69 +/- 0.12 to 4.95 +/- 0.14 cm; both P < 0.01), but not young adults (left ventricular end-diastolic volume from 107 +/- 7 to 111 +/- 7 ml and left ventricular internal diameter in diastole from 4.70 +/- 0.10 to 4.78 +/- 0.10 cm). Indices of left ventricular contractility (ejection fraction, myocardial acceleration during isovolumic contraction, and peak systolic mitral annulus velocity) were unchanged during cooling in both young and older adults. Collectively, these data indicate that cooling increases left ventricular preload, without affecting left ventricular contractility in older but not young adults. Greater increases in preload and afterload during cooling in older adults contribute to greater increases in indices of myocardial oxygen demand and may help explain the increased risk of cardiovascular events in cold weather.
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