Arterial oxygen saturation and heart rate variation during breath-holding: comparison between breath-hold divers and controls.

Breath-holding induces cardiovascular responses, notably bradycardia and peripheral vasoconstriction, which are known collectively as the diving response. This response is oxygen-conserving, i.e.

[Ventilatory adaptations for breath holding in divers].

The length of breath-hold duration in divers is dependant on a number of interacting variables which include mechanical factors (lung volumes), chemical factors (sensitivity to hypoxia and hypercapnia), non-chemical factors (involuntary muscular contractions), psychological factors (motivation, stress, competition) and various extrinsic factors (training, muscular exercise). These stimulus provoke the unpleasant sensation of an urge to breathe at the termination point of the breath hold. Training and experience produces adaptations in divers which decreases sensitivity to CO(2) and which delays and minimises the involuntary contractions of respiratory muscles provoked by the absence of respiratory movements.

Heart rate variation after breath hold diving with different underwater swimming velocities.

Background: The aim of this study was to demonstrate the kinetics of heart rate and blood lactate level obtained after repeated short breath holds with muscular effort in a swimming pool.

Experimental Design: each subject had to perform a series of breath hold diving at rest and three series for different underwater swimming velocities. A series corresponded to six dives of a 30 sec duration separated by a recovery period of 30 sec.

Ventilatory responses to hypercapnia in divers and non-divers: effects of posture and immersion.

The aim of this study was to determine the effects on respiratory drive of two factors, one mechanical (lung volume) and one chemical (sensitivity to hypercapnia), that are involved in determining the breath-hold duration (BHD). Functional residual capacity was measured by helium dilution with the subject seated in air, seated in water and in the prone position in water. Hyperoxic hypercapnia rebreathing (Read's method) was carried out under identical environmental conditions to assess the effects of CO2 pressure on respiratory centre output by measuring ventilation, mean inspiratory flow and occlusion pressure.

Breath-holding time: effects of non-chemical factors in divers and non-divers.

Two main factors (chemical and non-chemical factors) are involved in the determination of breath-holding time (BHT). Earlier studies have shown that chemical factors can be modified by training. The aim of this study was to establish whether BHT can be lengthened or shortened by changes in non-chemical factors according to the degree of training of the divers.