Role of hypocapnia in the blood lactate accumulation during acute hypoxia

High ventilation breathwork practices: An overview of their effects, mechanisms, and considerations for clinical applications

High Ventilation Breathwork (HVB) refers to practices employing specific volitional manipulation of breathing, with a long history of use to relieve various forms of psychological distress. This paper seeks to offer a consolidative insight into potential clinical application of HVB as a treatment of psychiatric disorders. We thus review the characteristic phenomenological and neurophysiological effects of these practices to inform their mechanism of therapeutic action, safety profiles and future clinical applications. Clinical observations and data from neurophysiological studies indicate that HVB is associated with extraordinary changes in subjective experience, as well as with profound effects on central and autonomic nervous systems functions through modulation of neurometabolic parameters and interoceptive sensory systems. This growing evidence base may guide how the phenomenological effects of HVB can be understood, and potentially harnessed in the context of such volitional perturbation of psychophysiological state. Reports of putative beneficial effects for trauma-related, affective, and somatic disorders invite further research to obtain detailed mechanistic knowledge, and rigorous clinical testing of these potential therapeutic uses.

Age-dependent metabolic effects of repeated hypoxemia in piglets

The aim of this study was to determine whether repeated exposure to hypoxemia would modify the response to hypoxemia during maturation. We exposed piglets to three 1-h cycles of hypoxemia (PaO2 = 30 to 35 mmHg; 1 mmHg = 133.3 Pa) at 1 week (n = 9), 2-3 weeks (n = 10), and 4-5 weeks of age (n = 10). O2 consumption (VO2) and CO2 production (VCO2) were measured, and alveolar ventilation (VA) was derived from VCO2 and PaCO2. Levels of lactic acid (lactate) and serum catecholamines were also measured. With hypoxemia, time had a significant effect on VO2 and body temperature in an age-dependent fashion: that is, whereas the 1 week group and the 4-5 week group showed both variables decreasing over time, the 2-3 week group showed no drop in VO2 and a small increase in body temperature over time. Lactate levels increased with hypoxemia in all animals during the first exposure. However, with repeated exposures to hypoxemia, only the 2-3 week group continued to increase its lactate levels. Furthermore, the changes in lactate levels paralleled the changes in epinephrine levels with hypoxemia. We found, too, that although VA increased significantly with hypoxemia in all animals, this change was not modified by age or repeated exposures. No significant effects of age or repeated exposures were found in the cardiovascular response to hypoxemia. We concluded that, from a metabolic viewpoint, after repeated exposures to hypoxemia the 2-3 week animals responded differently.Key words: metabolic rate, lactic acid, maturation, catecholamines.

Net uptake of lactate by rabbit hindlimb during hypoxia

Lactate uptake by normoxic tissues is a pH-dependent phenomenon that occurs with increases in arterial lactate concentration. In this study we sought to determine the effect of hypoxia on lactate uptake by the rabbit hindlimb at different arterial blood pH (pHa). Two groups of rabbits were subjected to 20 min of arterial hypoxemia (PaO2 approximately 20 mm Hg). One group was allowed to maintain normal pHa (approximately 7.40 to 7.45; n = 5), whereas the other group was hyperventilated, resulting in hypocarbia and alkalemia (pHa > 7.50; n = 5). Lactate uptake was computed from measurements of femoral blood flow and the arterio-venous lactate difference. We found decreases in hindlimb O2 consumption during hypoxemia from 0.79 +/- 0.08 to 0.33 +/- 0.06 ml/min in the normal pH group (p < 0.01) and from 0.49 +/- 0.06 to 0.24 +/- 0.02 ml/min in the high pH group (p < 0.01). At that time there was net uptake of lactate by the hindlimb of the normal pH group (8.1 +/- 2.0 mumol/min; p < 0.001) and lactate release by the alkalemic group (1.61 +/- 1.0 mumol/min). Furthermore, hindlimb lactate uptake was associated with increased glucose consumption (p < 0.001). We hypothesize that the mechanisms responsible for lactate uptake by resting skeletal muscle during hypoxia may be similar to those that regulate lactate uptake during normoxic exercise.

Severe hypoxia decreases oxygen uptake relative to intensity during submaximal graded exercise

The effect of severe acute hypoxia (fractional concentration of inspired oxygen equalled 0.104) was studied in nine male subjects performing an incremental exercise test. For power outputs over 125 W, all the subjects in a state of hypoxia showed a decrease in oxygen consumption (VO2) relative to exercise intensity compared with normoxia (P < 0.05). This would suggest an increased anaerobic metabolism as an energy source during hypoxic exercise. During submaximal exercise, for a given VO2, higher blood lactate concentrations were found in hypoxia than in normoxia (P < 0.05). In consequence, the onset of blood lactate accumulation (OBLA) was shifted to a lower VO2 (VO2 1.77 l.min-1 in hypoxia vs 3.10 l.min-1 in normoxia). Lactate concentration increases relative to minute ventilation (VE) responses were significantly higher during hypoxia than in normoxia (P < 0.05). At OBLA, VE during hypoxia was 25% lower than in the normoxic test. This study would suggest that in hypoxia subjects are able to use an increased anaerobic metabolism to maintain exercise performance.

Serial determinations of blood lactate in respiratory distress syndrome

Blood lactate was measured 4-hourly in 21 newborn babies with respiratory distress syndrome, of whom 13 survived and 8 died. In general, lactate levels were higher in babies who died than in survivors, but there were inconsistencies which were uninterpretable if only a single estimation were made in a baby. Analysis of serial determinations showed that all patients in whom the lactate level never exceeded 35 mg/100 ml survived, and babies with high but falling values also did well. Only those who had rising lactate values, even if initially normal, died. In most cases a high or normal P_ao₂ was associated with normal or decreasing lactate level; but babies with P_ao₂ below 60 mmHg had often also normal or decreasing lactate levels. Some babies had high and increasing lactate levels despite having normal P_ao₂. In order to use lactate levels for prognosis in respiratory distress syndrome (RDS) serial determinations are required. It is concluded that there may be a wide range of hypoxaemia without oxygen deficit in body tissues, so that it is not possible to define a `lower acceptable P_ao₂' which will define adequate tissue oxygenation.

Acid-base balance in acute gastrointestinal bleeding

Acid-base balance has been studied in 21 patients with acute upper gastrointestinal bleeding. A low plasma bicarbonate concentration was found in nine patients, accompanied in each case by a base deficit of more than 3 mEq/litre, indicating a metabolic acidosis. Three patients had a low blood pH. Hyperlactataemia appeared to be a major cause of the acidosis. This was not accompanied by a raised blood pyruvate concentration. The hyperlactataemia could not be accounted for on the basis of hyperventilation, intravenous infusion of dextrose, or arterial hypoxaemia. Before blood transfusion it was most pronounced in patients who were clinically shocked, suggesting that it may have resulted from poor tissue perfusion and anaerobic glycolysis. Blood transfusion resulted in a rise in lactate concentration in seven patients who were not clinically shocked, and failed to reverse a severe uncompensated acidosis in a patient who was clinically shocked. These effects of blood transfusion are probably due to the fact that red blood cells in stored bank blood, with added acid-citrate-dextrose solution, metabolize the dextrose anaerobically to lactic acid. Monitoring of acid-base balance is recommended in patients with acute gastrointestinal bleeding who are clinically shocked. A metabolic acidosis can then be corrected with intravenous sodium bicarbonate.