Biomedical subjects

Jonathan E Wingo

Publications and source records attributed to Jonathan E Wingo.

4 recordsLinked to original sources

PubMed2006

Body cooling attenuates the decrease in maximal oxygen uptake associated with cardiovascular drift during heat stress.

Previous research suggests cardiovascular drift (CV drift) is associated with decreased maximal oxygen uptake (VO(2)(max)) during heat stress, but more research manipulating CV drift with subsequent measurement of VO(2)(max) is needed to assess whether this relationship is causal. To assess causation, VO(2)(max) was measured during the same time interval that CV drift occurred (between 15 and 45 min of submaximal exercise under different conditions of body cooling intended to manipulate CV drift). Ten men completed a control graded exercise test (GXT) in 22 degrees C to measure VO(2)(max) then on separate occasions they cycled in 35 degrees C at 60% VO(2)(max) for 15 min (15 max), 45 min with no cooling (NC), and 45 min with fan airflow (FAN) beginning at approximately 18 min into exercise, and each bout was immediately followed by a GXT to measure VO(2)(max) In NC, VO(2)(max) decreased 18%, heart rate (HR) increased 16%, and stroke volume (SV) fell 12% (P < 0.05) from min 15 to min 45. In FAN, VO(2)(max) fell less (5.7%, P < 0.05) , HR rose less (4%, P < 0.05) and SV decreased less (3%, P < 0.05) from 15 to 45 min. The fall in VO(2)(max) associated with CV drift during exercise in a hot environment is attenuated with body cooling via fan airflow. The findings support the notion that a causal link exists between CV drift that occurs during prolonged exercise in a hot environment and a decrease in VO(2)(max).

Adaptation, Physiological↗

PubMed2006

Fluid ingestion attenuates the decline in VO2peak associated with cardiovascular drift.

INTRODUCTION/PURPOSE: This study investigated whether manipulation of cardiovascular drift (CV drift) by changing exercise duration or by fluid ingestion is associated with altered peak oxygen uptake VO(2peak). METHODS: VO(2peak) was measured in 11 trained men immediately after they cycled at 60% control VO(2max) in 30 degrees C, 40% relative humidity for 15, 60, and 120 min with no fluid (15 NF, 60 NF, 120 NF) or 120 min with fluid (120 F). Stroke volume (SV), heart rate (HR), and related measures were measured in 120 NF and 120 F at 15, 60, and 120 min. RESULTS: Body mass decreased 0.7, 2.3, and 3.7% in 120 F, 60 NF, and 120 NF. SV at the end of submaximal exercise and VO(2peak) measured immediately thereafter were reduced significantly (P < 0.05) from 15-min values in 120 NF (13.8 and 8.7%) but not in 60 NF (4.6 and 1.2%) or 120 F (2.1 and 1.9%). CONCLUSIONS: The progressive decline in SV during prolonged, constant-rate submaximal exercise in a warm environment, reflective of increased cardiovascular strain associated with hyperthermia, dehydration, and other changes that occur over time, reduces VO(2peak). Fluid ingestion improves performance in prolonged exercise, in part, by mitigating the decline in SV and its determinants, and preserving VO(2peak).

Adult↗

PubMed2006

Maximal oxygen uptake after attenuation of cardiovascular drift during heat stress.

INTRODUCTION: Exercise intensity is often regulated in hot conditions by maintaining a constant target heart rate (HR) to counteract increased physiological strain and thereby avoid premature fatigue. It is unknown, however, whether the HR-percent maximal oxygen uptake (%VO2max) relationship is maintained during prolonged exercise in the heat when the rise in HR concomitant with cardiovascular drift (CV drift) is eliminated by lowering exercise intensity. The purpose of this study was to determine if VO2max is reduced when exercise intensity and absolute VO2 are lowered by a magnitude sufficient to reduce CV drift and maintain constant HR during prolonged exercise in the heat, and thereby examine if the HR-%VO2max relationship is preserved. METHODS: Seven men cycled at 60% VO2max in 35 degrees C for 15 min (one trial) and 45 min (two trials) while HR rose over time (HRvar) or remained constant (HRcon). VO2max was measured immediately after the 15 and 45 min trials to correspond with the same time interval in which CV drift occurred. RESULTS: Power output decreased 37%, VO2 decreased 24%, and VO2max decreased 7.5% from 15 to 45 min in HRcon, while HR remained the same. In HRvar, HR increased 13%, SV decreased 10%, and VO2max decreased 15%. DISCUSSION: %VO2max was decreased from approximately 60% to 50% to hold HR constant in these conditions, so the HR-%VO2max relationship was not preserved in the absence of CV drift. Attenuating CV drift by lowering exercise intensity only partially eliminated the reduction in VO2max after prolonged exercise in the heat.

Acclimatization↗

PubMed2005

Cardiovascular drift is related to reduced maximal oxygen uptake during heat stress.

INTRODUCTION/PURPOSE: This study investigated whether the progressive rise in heart rate (HR) and fall in stroke volume (SV) during prolonged, constant-rate, moderate-intensity exercise (cardiovascular drift, CVdrift) in a hot environment is associated with a reduction in VO(2max). METHODS: CVdrift was measured in nine male cyclists between 15 and 45 min of cycling at 60% VO(2max) in 35 degrees C that was immediately followed by measurement of VO(2max). VO(2max) also was measured after 15 min of cycling on a separate day, so that any change in VO(2max) between 15 and 45 min could be associated with the CVdrift that occurred during that time interval. This protocol was performed under one condition in which fluid was ingested and there was no significant body weight change (0.3 +/- 0.4%), and under another in which no fluid was ingested and dehydration occurred (2.5 +/- 1%, P < 0.05). RESULTS: Fluid ingestion did not affect CVdrift or change in VO(2max). A 12% increase in HR (151 +/- 9 vs 169 +/- 10 bpm, P < 0.05) and 16% decrease in SV (120 +/- 12 vs 101 +/- 10 mL.beat(-1), P < 0.05) between 15 and 45 min was accompanied by a 19% decrease in VO(2max) (4.4 +/- 0.6 vs 3.6 +/- 0.4 L.min(-1), P < 0.05) despite attainment of a higher maximal HR (P < 0.05) at 45 min (194 +/- 5 bpm) vs 15 min (191 +/- 5 bpm). Submaximal VO(2) increased only slightly over time, but VO(2max) increased from 63 +/- 5% at 15 min to 78 +/- 8% at 45 min (P < 0.05). CONCLUSION: We conclude CVdrift during 45 min of exercise in the heat is associated with decreased VO(2max) and increased relative metabolic intensity. The results support the validity of using changes in HR to reflect changes in relative metabolic intensity during prolonged exercise in a hot environment in which CVdrift occurs.

Adult↗