Journal of applied physiology
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Wrapping low-birth-weight neonates in a plastic bag prevents body heat loss. A bonnet can also be used, since large amounts of heat can be lost from the head region, but may provide too much thermal insulation, thus increasing the risk of overheating. We assessed the time required to reach warning body temperature (t38 degrees C), heat stroke (t40 degrees C), or extreme value (t43 degrees C) in a mathematical model that involved calculating various local body heat losses. ⋯ When endogenous heat production rises, t38 degrees C ranged between 75 and 287, t40 degrees C between 185 and 549, and t43 degrees C between 287 and 702 min. When this increase was accompanied by a fall in skin temperature, overheating risk was accentuated (37
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Phenylephrine decreases frontal lobe oxygenation at rest but not during moderately intense exercise.
Whether sympathetic activity influences cerebral blood flow (CBF) and oxygenation remains controversial. The influence of sympathetic activity on CBF and oxygenation was evaluated by the effect of phenylephrine on middle cerebral artery (MCA) mean flow velocity (Vmean) and the near-infrared spectroscopy-derived frontal lobe oxygenation (ScO2) at rest and during exercise. At rest, nine healthy male subjects received bolus injections of phenylephrine (0.1, 0.25, and 0.4 mg), and changes in mean arterial pressure (MAP), MCA Vmean, internal jugular venous O2 saturation (SjvO2), ScO2), and arterial PCO2 (PaCO2) were measured and the cerebral metabolic rate for O2 (CMRO2) was calculated. ⋯ MAP increased after the administration of phenylephrine during low-intensity exercise (approximately 15%), but this was attenuated (approximately 10%) during high-intensity exercise (P<0.001). The reduction in ScO2 after administration of phenylephrine was attenuated during low-intensity exercise (-5%, P<0.001) and abolished during high-intensity exercise (-3%, P=not significant), where PaCO2 decreased 7% (P<0.05) and CMRO2 increased 17% (P<0.05). These results suggest that the administration of phenylephrine reduced ScO2 but that the increased cerebral metabolism needed for moderately intense exercise eliminated that effect.
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Restriction of total lung capacity (TLC) is found in some obese subjects, but the mechanism is unclear. Two hypotheses are as follows: 1) increased abdominal volume prevents full descent of the diaphragm; and 2) increased intrathoracic fat reduces space for full lung expansion. We have measured total intrathoracic volume at full inflation using magnetic resonance imaging (MRI) in 14 asymptomatic obese men [mean age 52 yr, body mass index (BMI) 35-45 kg/m2] and 7 control men (mean age 50 yr, BMI 22-27 kg/m2). ⋯ The difference in gas volume at TLC between the six obese men with restriction, TLC<80% predicted (OR), and the eight obese men with TLC>80% predicted (ON) was 26% predicted TLC. Mediastinal volume was similar in OR (1.84 liter) and ON (1.73 liter), but total intrathoracic volume was 19% predicted TLC smaller in OR than in ON. We conclude that the major factor restricting TLC in some obese men was reduced thoracic expansion at full inflation.