Diurnal variation in the control of ventilation in response to rising body temperature during exercise in the heat

Higher evening metabolic responses contribute to diurnal variation of self-paced cycling performance

This study examined the effect of time of day (TOD) on physical performance, and physiological and perceptual responses to a 10-km cycling time trial (TT_10km). Twelve physically trained subjects (20.3 ± 1.2 years, 74.3 ± 7.4 kg, 179.7 ± 5.5 cm) completed, in a randomized order, a TT_10km in the morning and in the evening. Intra-aural temperature (IAT) was measured at rest and following the TT_10km. Completion time, power output (PO), rating of perceived exertion (RPE), heart rate (HR), minute ventilation (V̇E), oxygen uptake (V̇O₂), carbon dioxide production (V̇CO₂) and respiratory exchange ratio (RER) were assessed every km during the TT_10km. Blood lactate concentration [La] and blood glucose concentration [Glu] were assessed before, during and immediately after the TT_10km. Faster completion time (Δ = 15.0s, p = 0.03) and higher IAT (Δ = 0.33°C, p = 0.02 for pre-TT_10km) were obtained in the evening compared to the morning with a significant correlation between Δ completion time and Δ IAT at post-TT_{10 km} (r = -0.83, p = 0.04). V̇O₂, [La] and [Glu] increased significantly during both test sessions (p < 0.001) with higher values in the evening compared to the morning (p = 0.015, p = 0.04, p = 0.01, respectively). However, the remaining parameters were found to be only affected by the TT_10km (p < 0.001). The TT_10km generates a higher V̇O₂ and higher [La] and [Glu] responses, contributing to a better cycling performance in the evening compared to the morning. The similar magnitude of the TOD effect on completion time and IAT at post-TT_10km confirms that core temperature is one of the underlying factors contributing to the diurnal variation in physical performance.

Difference of body surface temperature in stable chronic obstructive pulmonary disease patients with different degree of airflow limitation

BACKGROUND

This study aimed to investigate the changes of body surface temperature of stable chronic obstructive pulmonary disease (COPD) patients and explore its clinical significance for the progression of COPD.

OBJECTIVES

The aim of this study was to explore the correlation between body surface temperature and disease severity in COPD patients.

METHODS

From May 2015 to May 2016, the patients who were diagnosed as COPD at stable phase (n = 148) were enrolled in this study. The subjects in control group (n = 49) were healthy people. The patients' general condition modified Medical Research Council (mMRC) dyspnea scale and the COPD assessment test (CAT) score were recorded, and pulmonary function of patients was determined. Back average temperature measurement was made using a thermal infrared imager (DT-9875, CEM, China).

RESULTS

Patients in the COPD group had significantly lower mean temperatures of the back than those in the control group. The mean temperature of the back presented a decreased tendency with the aggravation of airflow limitation. Correlation analysis revealed that in the COPD group, the back temperature was negatively correlated with smoking index and mMRC score. FEV1%, FVC% and FEV1/FVC were positively correlated with pulmonary function. Smoking showed a tendency to lower the back temperature of COPD patients.

CONCLUSIONS

This study preliminarily suggested that the body surface temperature of COPD patients decreased compared with that of healthy people, which may be associated with the dysfunction of autonomic nerve, increased basal metabolic rate, metabolic syndrome and peripheral nerve injury in COPD patients.