What happens to metabolic rate when breath-holding in humans?

Davis, Chloe (2019). What happens to metabolic rate when breath-holding in humans? University of Birmingham. M.Sc.

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Abstract

Objective:

Despite suggestions of a human dive response, a few studies > 50 years ago concurred that humans do not reduce metabolic rate when breath-holding. However, these studies had limited participant numbers, did not account fully account for oxygen consumed from the blood, or consider additional oxygen supplied to the blood from contraction of the spleen. Nor did they consider that the loss of respiratory muscle contraction alone may result in a reduction in metabolic rate. Here we are address these limitations.

Methods:

In 20 subjects we measured metabolic rate at rest, over the course of breath-holds, and in the period following breath-holds from air and 60% oxygen using Douglas bags. In our investigation we have also 1) measured SpO2 and included extra oxygen consumed from the blood, 2) accounted for additional oxygen supplied to the blood from contraction of the spleen, and 3) measured the oxygen requirement for breathing via mechanical ventilation (n = 10).

Results:

Metabolic rate at rest was 227 ± 39 millilitres.oxygen · minute-1 STPD (n = 20). The metabolic cost of breathing was 60 ± 40 SD millilitres oxygen · minute-1, STPD (n =10). Over breath-holds from air and after accounting for arterial desaturation and spleen contraction, metabolic rate slightly fell to 152 ± 48 SD millilitres oxygen · minute-1, STPD (p < 0.001 vs SpO2, n = 20) (p < 0.05 vs mechanical ventilation, n = 10). When breath-holding from oxygen, when arterial desaturation does not occur but still accounting for contraction of the spleen, reductions in metabolic rate were potentiated and it fell to 96 ± 26 SD millilitres oxygen · minute-1, STPD (p < 0.001 vs rest, n = 20) (p < 0.001 vs breath-hold from air, n = 20) (p < 0.01 vs mechanical ventilation, n = 10).

Conclusions:

For the first time we show that metabolic rate falls when breath-holding in humans, even after accounting for oxygen consumed from the blood and additional oxygen consumed from the blood by spleen contraction. When breath-holds were prolonged with oxygen, reductions in metabolic rate were accentuated. Such reductions are greater than measured reductions associated with the absence of respiratory muscle contraction. Whilst suggestions of the dive response resurface, detailed literature examination highlights humans do not exhibit a response of a magnitude comparable to that of diving mammals.

Type of Work:

Thesis (Masters by Research > M.Sc.)

Award Type:

Masters by Research > M.Sc.

Supervisor(s):