Cardiovascular and cerebrovascular responses to lower body negative pressure in smokers

Miller, Andre'
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The purpose of this study was to document the autonomic physiological responses to lower body negative pressure (LBNP) in smokers and non-smokers. A total of 20 subjects, (n=10) smokers and (n=10) non-smoker, (26 ± 5 years, 169 ± 10cm,74 ± 13 kg; mean ± SE) participated in this study. A standard 4-lead ECG, finger photoplethysmography, transcranial Doppler ultrasound and a facemask with an infrared carbon dioxide sensor were used to record dependent variable data. A lower body negative pressure chamber was decompressed at a rate of 3mmHg per minute over the course of 20 minutes from 0mm Hg to -60mmHg. Arterial pressures, stroke volume, cardiac output, heart rates and middle cerebral flow velocities were recorded every 2 minutes. Significant reductions (p <.05) were observed for the effect of LBNP in both smokers and non-smokers for systolic and mean arterial pressures, stroke volume, cardiac output, systolic, diastolic and mean middle cerebral arterial velocities and carbon dioxide percentages. No effect was observed for the condition of smoking status on arterial pressures, stroke volume, cardiac output, heart rates, total peripheral resistance, middle cerebral flow velocities, expiratory carbon dioxide percent, respiratory rates or tolerance to LBNP. However, between group absolute value differences were large and p-values were small for heart rate, (F (1,18) =1.46, P=.25, cardiac output, (F (1,18) =1.69, P = .21 and stroke volume, (F (1,18) =3.42, P=.08. Large differences among certain variables, while not statistically different, may in fact be clinically relevant.

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Autonomic, Cardiology, Cerebrovascular, Hemodynamics, Hemorrhage, Physiology
Health and Kinesiology