The Effect of Intense Passive Apnea in the Acid-Base Balance and Electrolytes

Abstract

The aim of this study was to investigate the disturbances of the acid-base balance and electrolyte disorders in healthy individuals in the greatest passive apnea (prior to apnea and prior to first inhalation). The changes of the acid-base balance, the serum potassium and calcium levels as well as the disturbances of the cardiac rhythm were studied in a group of 15 healthy males aged 18 to 41 years old. Seven individuals part of the original group participated in a second trial. Following the initial apnea trial the individuals were allowed to 2–3 free inhalations and a second passive apnea effort was performed. The same parameters were measured in the second effort. In the primary effort the apnea duration was 170 ± 53 s (mean ± SD). The results received prior to the effort and immediately before the end of the apnea (paired t-test), showed no significant changes in the blood pH. The PaCO₂ increased significantly, the PaO₂ decreased significantly, blood bicarbonate increased significantly, the hemoglobin oxygen saturation decreased significantly. In addition the serum potassium and calcium levels decreased significantly. In the subgroup (7 individuals) the second effort of apnea lasted 50–70 s and showed no significant changes in the blood pH. The same changes concerning PaCO₂ and blood bicarbonate were observed in the first and second effort of passive apnea. The serum potassium and calcium levels as well as the hemoglobin oxygen saturation showed no significant changes. During the initial effort of apnea all men presented bradycardia, which was followed by tachycardia immediately after the end of the effort. One individual, whose effort lasted 290 s suffered intense tachycardia, cyanosis, convulsions, and loss of consciousness. It is concluded that during an intense effort of passive apnea: (a) the blood PaCO₂ is significantly increased, as well as the blood bicarbonates, (b) the PaO₂, the hemoglobin oxygen saturation and the serum potassium and calcium levels are significantly decreased, (c) the cardiac rate is significantly decreased, and (d) the second effort of apnea, following immediately the initial one, is sorter in duration and produces similar or milder changes of the above parameters.

• Apnea passive
• Acid-base balance
• Serum potassium
• Serum calcium pH
• Bicarbonate

Introduction

Many times divers expose themselves to danger following their urge to accomplish different tasks during a dive. Usually they ignore the physiology of breathing and details that are related to blood gases changes. Other times for demonstration purposes reach their endurance limits exposing themselves in great risk. Bibliography data concerning apnea during dynamic apnea as well as passive apnea are limited. The present study examines the influence of intense passive apnea in blood gases and serum electrolyte levels.

Patients and Methods

Fifteen male volunteers, aged from 18 to 42 years (median 22 years), athletes, specialized in diving, most of them students of physical education were included in the study. The apnea trial was performed in supine position. The procedure was the following: After two medium duration apnea efforts and before the major apnea effort the first blood sample was drawn. The second blood sample was drawn just before the end of the effort. The subgroup (7 males) after the major apnea effort received 2 to 3 free inhalations and proceeded in a second apnea effort.

The blood sample was drawn by the redial artery, before the beginning and before the end of the apnea effort. The changes of blood gases (PaO₂, PaCO₂, oxygen hemoglobin saturation), the , the serum potassium and calcium levels were studied during the effort of passive apnea.

The blood gases were analyzed by an automatic analyzer (348/Chiron, USA), while the potassium and calcium with ion selectively analyzer (Dimension A.R., Acsess, USA). The hemoglobin oxygen saturation was analyzed by analyzer (In Vivo, 4500 Plus3, USA). The apnea duration was measured by a timer. The cardiac rhythm was checked continuously by an electrocardiograph recording.

Results

The duration of the first apnea effort varied from 80 to 290 s (170 ± 53), while duration of the second apnea effort was shorter varying from 50 to 70 s (59.3 ± 8.4) (p = 0.0001). By the examinations of the blood samples (received before the beginning and just before the first apnea effort) no significant changes in the blood pH were shown, while the PaCO₂ and the increased significantly (p = 0.009 and p = 0.023 respectively). The PaO₂, the hemoglobin oxygen saturation, the serum potassium, and calcium levels were decreased significantly (p = 0.0001, p = 0.001, p = 0.005, p = 0.029 respectively) (Table 1). The examinations of the blood samples, received before the beginning of the first apnea effort and just before the end of the second apnea effort, showed milder changes. The hemoglobin oxygen saturation, the serum potassium, and calcium levels showed no significant changes, while the PaCO₂ and the were increased significantly, and PaO₂ decreased significantly (Table 2).

Table 1. Changes of blood pH, PaCO₂ (mmHg), PaO₂ (mmHg), (mEq/L), Hb oxygen saturation (%), serum potassium (mEq/L), and calcium levels (mmol/L) (before the first effort of apnea and before the end of the effort)

	pH		PaCO2		PaO2				Hb oxygen saturation		Serum potassium		Serum calcium
n	Before	After	Before	After	Before	After	Before	After	Before	After	Before	After	Before	After
1	7.385	7.36	45.8	52.5	92.2	50.2	26.8	29	96.9	83.6	3.9	3.85	1.21	1.14
2	7.415	7.377	40.1	47.8	78.9	57.8	25.1	27.5	95.8	89.3	4.1	3.78	1.36	1.36
3	7.441	7.416	38.1	41.9	96.8	49.2	25.4	26.4	96.8	85.4	3.93	3.88	1.24	1.14
4	7.382	7.399	41	47.1	90.8	55.4	24.3	28.5	96.8	88.6	4.25	3.9	1.39	1.16
5	7.414	7.352	41.4	49.7	95.3	63	25.9	26.9	97.4	90.9	4.06	3.7	1.19	1.25
6	7.428	7.36	39.1	47.6	91	55.6	25.2	26.3	97.2	87.6	4.15	4.1	1.23	1.16
7	7.436	7.392	39.5	45.3	83.5	63.6	26	26.9	96.6	92.1	3.75	3.84	1.28	1.09
8	7.437	7.407	42.9	51.2	98.9	55.1	28.3	31.5	97.7	88.5	3.89	3.58	1.18	1.08
9	7.448	7.393	41.9	44.2	87.3	51.4	28.4	26.3	97	86.1	3.78	3.64	1.26	1.08
10	7.396	7.43	42.1	40.8	82.9	56	25.3	26.4	96.1	90	3.92	3.89	1.13	1.26
11	7.399	7.441	39.4	39.9	92.5	46.1	23.8	25.3	97.1	83.8	4.2	4.09	1.22	1.17
12	7.414	7.41	43.4	45.1	91.4	60	27.1	28	97.1	91.1	3.45	3.56	1.23	1.22
13	7.418	7.39	42.7	44.8	99.3	68.4	27	26.5	97.6	93.5	3.57	3.3	0.99	0.79
14	7.408	7.469	44.7	37.4	85.7	25	27.6	26.5	96.5	49.6	3.5	3.08	1.15	1.11
15	0	7.426	43.5	42.9	99.3	57.2	27.6	27.6	97.6	90.3	3.64	3.65	1.14	0.91
Mean	7.42	7.4	41.7	45.2	91.1	54.3	26.3	27.3	97	86	3.87	3.73	1.21	1.15
(±)SD	0.02	0.33	2.2	4.2	6.4	10	1.41	1.6	0.5	10.5	0.25	4.28	0.14	0.16
p =	NS		0.009		0.0001		0.023		0.001		0.005		0.029

Table 2. Changes of blood pH, PaCO₂ (mmHg), PaO₂ (mmHg), (mEq/L), Hb oxygen saturation (%), serum potassium (mEq/L), and calcium levels (mmol/L) (before the first effort of apnea and before the end of the second effort)

	pH		PaCO2		PaO2				Hb oxygen saturation		Serum potassium		Serum calcium
n	Before	After	Before	After	Before	After	Before	After	Before	After	Before	After	Before	After
1	7.437	7.355	42.9	53.9	98.9	73.5	28.3	29.4	97.7	93.9	3.89	3.54	1.18	0.98
2	7.448	7.415	41.9	46.1	87.3	66	28.4	28.9	97	93.2	3.78	3.68	1.26	1.06
3	7.396	7.395	42.1	43.5	82.9	69.6	25.3	26	96.1	93	3.92	3.81	1.13	1.16
4	7.399	7.472	39.4	37.2	92.5	31.4	23.8	26.7	97.1	64.8	4.2	4.06	1.22	1.28
5	7.414	7.395	43.4	47.5	91.4	75.8	27.1	28.4	97.1	95	3.45	3.57	1.23	1.27
6	7.418	7.402	42.7	43.8	99.3	91.8	27	26.6	97.6	97	3.57	3.29	0.99	0.98
7	7.419	7.422	43.5	45.5	99.3	68.1	27.6	29	97.6	93.9	3.64	3.55	1.14	1.21
Mean	7.42	7.41	42.3	45.4	93.1	68	26.8	27.2	97.2	90.1	3.8	3.6	1.16	1.13
(±)SD	0.02	0.05	1.4	5	6.5	18.3	1.7	1.4	0.6	11.2	0.3	0.2	0.09	0.13
p =	NS		0.093		0.01		0.031		NS		NS		NS

The comparison of pulses/min before the beginning (81.3 ± 13.7), and just before the end (67.2 ± 10) of the apnea effort showed significantly reduction in all volunteers (paired t-test, p = 0.0001). It is noted that all volunteers presented tachycardia after the end of the effort, but no type of arrhythmias or other clinical event was observed. One volunteer presented intense tachycardia, cyanosis, loss of consciousness (he fully recovered).

Discussion

The most important stimulators of the respiration are the central chemoreceptors, which are stimulated by changes of blood PaCO₂ or H⁺. The increase of alveolar partial pressures of CO₂ causes increase of carbon dioxide, which is transferred to the brain via carotid arteries and the vertebral basilar system. The CO₂ easily reaches through the cerebroblood barrier and acidifies the cerebrospinal fluid (CSF). It is important to note that the changes of the CSF pH at any level of PaCO₂ are more intense than the corresponding changes of blood pH since CSF does not contain significant quantities of buffers, capable to neutralize the H⁺. However the mechanism responsible for the cell response to the CSF acidic pH that causes an increase in breathing/minute is not yet fully specified but it seems that the cells responsive to acidic pH are located close to the lateral ventricles of the brain.[[1]]

The respiratory system is also influenced by the decrease of PaO₂, which is almost exclusively detected by the peripheral chemoreceptors (carotid bodies and aortic arc). None the less, a decrease of PaO₂ does not constitute the most important stimulator to increase breathing in normal conditions. Thus, a mild decrease of PaO₂ stimulates the peripheral chemoreceptors. A decrease below 60 mmHg causes an increase of alveolar ventilation, which is intensified by the progressive hypoxia.[[1]]

Stanek et al. measured the hemoglobin oxygen saturation (in arterial blood) continuously during the dive in apnea conditions and concluded that the mean was 73% (after a mean of 69 s of apnea) in women who remained in apnea as long as they could.[[2]] In our study in conditions of passive apnea, the duration of apnea was explicit longer and the mean of decrease of hemoglobin oxygen saturation was lower. In the subgroup, that participated in the second effort of intense apnea, the apnea duration was shorter and with milder changes in blood gases and serum electrolytes. It is important to note that in such cases the PaCO₂ change is higher. Diving experts report that an insistence and long lasting effort of apnea puts such strain of the body, that 30 to 40 min are required for the O₂ and CO₂ to be restored to the normal levels. It is obvious that dives that take place every 2–3 min do not allow blood gases to be restored to normal levels before the next dive. Considering the conditions that exist during the dives, progressively PaCO₂ increases and hypercapnia is a fact. It must be underlined that deep and fast breathing does not help overcome the problem of increasing partial pressure of CO₂.

There are only few studies that refer to blood gases and acid–base balance in conditions of passive apnea. However the blood gases, the acid–base balance as well as the serum lactate were studied in seven healthy women athletes during intense exercise (dynamic apnea). At the end of the apnea significant decrease was found of pH, PaO₂, and hemoglobin oxygen saturation. The PaCO₂ and were significant increase.[[3]] These results are in agreement with our study because lactate was not produced in the effort of passive apnea as it was in dynamic apnea studied by Matheson and McKenzie.[[3]]

Other investigators describe a change of serum electrolyte levels that was a fact also at our study. The change of serum potassium is probably due to small decrease of pH and its redistribution from extracellular to intracellular space. The most normal and expected response in apnea effort is the decrease of cardiac rhythm (bradycardia) and selective arterial constriction. The cardiac output redistributed, so that the blood flow in the heart and the brain is increased while the distribution in most viscera, nonactivated muscles, and the skin is decreased.

The bradycardia at apnea condition is a normal protective mechanism that aims in the decrease of oxygen consumption[[4]]and is termed “the mammals dive reflex.”[[5]] However, the mechanisms that lead in this change are not fully understood. Landsberg concluded that bradycardia during dives should be a physiologic maintenance reflex or a pathophysiologic respond to apnea.[[4]] Other researchers noted that apnea causes bradycardia to men and tachycardia to women and supposed that sex differences are involved in heart rate changes. They also supposed that two mechanisms are responsible for bradycardia, the respiratory basopressure receptors and the arterial chemoreceptors.[[6]] Manley argued that the factors that are involved in bradycardia at apnea are the environmental temperature, the physical condition of the diver, various respiratory volumes, the depth of dive and the position of the body during the effort.[[5]] Pan et al. ascertained that an increase in the blood quantity in aorta and the arteries by the end of the diastolic phase as well as a decrease venous reintroduction of blood causes an increase in peripheral resistance during the apnea.[[7]]

Finally the incident of loss of consciousness of one male athlete in our study must be underlined. The athlete who suffered cyanosis, convulsions, and loss of consciousness had reached the highest duration apnea of 290 s and exceeded himself. Impulse and enthusiasm may lead to irreversible conditions.

It is therefore concluded that an intense effort of passive apnea causes (a) significant increase of PaCO₂ and HCO_3, (b) significant decrease of PaO₂, hemoglobin oxygen saturation, serum potassium, and calcium levels, (c) a significant decreased of cardiac rhythm, (d) the second effort of apnea (immediately afterwards the first effort) is shorter in duration than the first, and (e) there are risks involved that must taken in consideration by the divers.