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Features of glossopharyngeal breathing in breath-hold divers

Departments of ¹Thoracic Medicine, and ²Cardiology, Concord Repatriation General Hospital, Concord, Sydney, New South Wales, Australia

Submitted 23 January 2006 ; accepted in final form 1 May 2006

	ABSTRACT

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One technique employed by competitive breath-hold divers to increase diving depth is to hyperinflate the lungs with glossopharyngeal breathing (GPB). Our aim was to assess the relationship between measured volume and pressure changes due to GPB. Seven healthy male breath-hold divers, age 33 (8) [mean (SD)] years were recruited. Subjects performed baseline body plethysmography (TLC_PRE). Plethysmography and mouth relaxation pressure were recorded immediately following a maximal GPB maneuver at total lung capacity (TLC) (TLC_GPB) and within 5 min after the final GPB maneuver (TLC_POST). Mean TLC increased from TLC_PRE to TLC_GPB by 1.95 (0.66) liters and vital capacity (VC) by 1.92 (0.56) liters (P < 0.0001), with no change in residual volume. There was an increase in TLC_POST compared with TLC_PRE of 0.16 liters (0.14) (P < 0.02). Mean mouth relaxation pressure at TLC_GPB was 65 (19) cmH₂O and was highly correlated with the percent increase in TLC (R = 0.96). Breath-hold divers achieve substantial increases in measured lung volumes using GPB primarily from increasing VC. Approximately one-third of the additional air was accommodated by air compression.

hyperinflation; lung packing; apnea diving

Looking for an advantage in a competitive sport, breath-hold divers have employed techniques that attempt to increase total lung capacity (TLC). This would allow for an increase in available O₂ stores for breath holding and gas stores for pressure equalization while diving. Many breath-hold divers perform glossopharyngeal breathing (GPB) at TLC both as a training exercise and immediately before a dive. They breathe to TLC and perform GPB to increase the amount of air in the lungs (14). This technique has features in common with the maneuvers that have been reported to be used by postpolio (7, 9) and tetraplegic patients (5). Patients with severe neuromuscular weakness while retaining good bulbar muscle function have found this an effective alternative to ventilator use during the day by assisting lung ventilation.

There has been limited evidence of breath-hold divers increasing TLC using GPB (13, 14, 17). A recent study on five breath-hold divers using GPB reported a TLC increase of 25% (11) from changes in vital capacity (VC) measurements, assuming a constant residual volume (RV).

We hypothesize that the increase in measured lung volume due to GPB, as previously reported, is the result of increasing VC, with no effect on RV, and is primarily the result of gas compression. We wished to measure TLC acutely after cessation of GPB to confirm that the measured volume increase was primarily due to gas compression, with an immediate return to baseline levels.

	METHODS

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Subjects.   Seven male competitive breath-hold divers who had previously practiced the technique of GPB were recruited. The subjects were nonasthmatic, were not current smokers, and did not have known or previous cardiac or lung disease.

Baseline "pre" lung function.   Sitting spirometric tests and single breath transfer factor for carbon monoxide were measured to confirm normal lung function. Baseline body plethysmography (TLC_PRE) (Sensormedics Vmax, Yorba Linda, CA) was then performed. All lung function tests were performed according to American Thoracic Society and American Association for Respiratory Care criteria (1, 3, 4) with predicted values derived from the recommendations of the European Community for Coal and Steel (8).

GPB plethysmography.   Sitting body plethysmography was recorded immediately following a maximal GPB maneuver at TLC (TLC_GPB). Once enclosed in the body plethysmograph, with tracing initiated by tidal volume, the subjects were instructed to come off the mouthpiece to perform the typical maneuver that allowed them to achieve what they believed to be their maximal lung volume with GPB, nose clip in situ. Then, without air leak, they returned to the mouthpiece and performed a slow expiratory VC maneuver to RV. Pants against a closed shutter for thoracic gas volume (V_TG) measurements were performed after a small inhalation (ERV_I), immediately post-VC. This technique was replicated for TLC_PRE and sitting plethysmography within 5 min of the final maneuver (TLC_POST). TLC was calculated by: TLC (BTPS) = V_TG – ERV_I + VC.

If they usually performed "warm-up" stretching and GPB, we allowed time for them to do so after the baseline measurement (no more than 10 min).

Mouth relaxation pressure.   The subjects were cognizant of the aims of measurement, and careful attention was given to obtaining open-glottis mouth relaxation pressure (P_Mouth). The pressure plateau was recorded at TLC_GPB with a fluid-filled catheter inserted through pursed lips with no air leak. The catheter was connected to a physiological pressure transducer (Spacelab Program module, Spacelabs, Redmond, WA), and measurements were repeated until two maximal reproducible efforts (within 2 cmH₂O) were obtained. The pressure transducer was calibrated by use of a water manometer and was zeroed at the level of the subject's mouth before each measurement.

Because all lung volume measurements are performed assuming barometric pressure (P_Baro), the application of Boyle's Law allowed us to estimate the compressive effect of the TLC_GPB lung volume compared with the open-glottis TLC_PRE lung volume. Any measured volume above TLC_PRE that was not due to compression of air can be assumed to be causing distention of the lung (TLC_Distended). Distention refers to the increased volume occupied by the lung in the hyperinflated and compressed state.

Boyle's law states that for a mass of gas with temperature held constant the pressure (P) is inversely proportional to the volume (V). Therefore the pressure-volume product in compressed state (P₁V₁) equals the product in atmospheric state (P₂V₂) with constant body temperature. Thus:

Therefore,

The percent change in volume from TLC_PRE values attributable to gas compression can then be estimated by

"Post" plethysmography.   Sitting plethysmography was repeated within 5 min of the final GPB maneuver (TLC_POST).

All V_TG curves and TLC, VC, and RV calculations were later verified by a second scientific officer who was not in attendance at testing. The body plethysmograph was calibrated before each testing session.

Supplemental O₂, resuscitation equipment, and medical personnel were available at all times.

The study was reviewed, approved, and conducted in accordance with the principles of the World Medical Association Declaration of Helsinki 2000, and this included the provision of fully informed consent. The Ethics Committee was Central Sydney Area Health Service Human Research Ethics Committee (Concord Rapatriation General Hospital zone).

Statistical analysis.   Results were expressed as means (SD). A two-tailed repeated-measures ANOVA was performed to analyze the change in measured lung volumes from TLC_PRE to TLC_GPB and TLC_PRE to TLC_POST. Significance was determined by use of a pairwise comparison and was considered significant if P < 0.02. The relationship between mouth relaxation pressure at TLC_GPB and change in measured lung volume, from TLC_PRE to TLC_GPB, was determined by use of a correlation analysis.

	RESULTS

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Seven male breath-hold divers were studied. The demographic and lung function data and breath-hold diving history of the study subjects are shown in Table 1. Baseline lung function in all subjects was within normal limits.

View larger version (12K): [in this window] [in a new window]   Fig. 1. Mean measured total lung capacity (TLC) with 1 SD bars, partitioned into vital capacity (VC) and residual volume (RV), in 7 breath-hold divers at baseline (TLCPRE) immediately following a maximal glossopharyngeal breathing maneuver at TLC (TLCGPB) and within 5 min of their final glossopharyngeal breathing maneuver (TLCPOST). *Compared with TLCPRE (P < 0.0001, repeated-measures ANOVA). **Compared with TLCPRE (P < 0.02, repeated-measures ANOVA).

View larger version (7K): [in this window] [in a new window]   Fig. 2. Plot of individual measurements () of mouth relaxation pressure at TLCGPB with the corresponding % change in measured volume from TLCPRE to TLCGPB. Solid line, correlation.

The mean recorded increase in TLC from TLC_PRE to TLC_GPB was 1.95 liters (range 1.23–3.01). The mean volume due to air compression was 31% of this measured volume increase and equates to 610 ml (BTPS). Therefore, the mean increase in TLC that is distention of the lung is estimated to be 1.34 liters (BTPS).

	DISCUSSION

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This study has measured the substantial increases in lung volumes that breath-hold divers can achieve using GPB as described previously (13, 14, 17). This was primarily from an increase in measured VC, with no change in RV. From average recorded mouth relaxation pressure measured at TLC_GPB, we estimate that 31% of the additional air was accommodated by air compression.

Conventionally TLC is the point of maximum inflation. This volume is reached when maximal inspiratory muscle tension is exerted. The increasing muscular disadvantage against an increasing chest wall and more importantly lung recoil is said to determine TLC (16).

To increase lung volume above normal TLC, GPB must overcome recoil pressures and distend the rapidly stiffening lung. This requires substantial pressure given the mouth relaxation pressures measured here range from 40 to 90 cmH₂O. GPB above TLC is limited by "discomfort" and reported to improve with training (W. Steyn, personal communication). This raises the possibility that recoil pressure at high lung volumes may be altered transiently by lung overdistension. This view is consistent with our finding that TLC_POST of all subjects measured in the 5-min period after GPB was increased outside expected normal intrasubject variation (1).

The concept of hysteresis explains the recoil pressure difference at a given lung volume depending on the volume history (i.e., during inflation or deflation) on a breath-by-breath basis (10). However, it is not inconceivable that, when lungs are distended by GPB beyond the normally obtained maximum inflation (i.e., TLC), the time course for lung and or chest wall recoil pressure recovery may be prolonged. Addressing this question, a previous report on a single elite breath-hold diver did not find a change in pulmonary compliance between normal and TLC_GPB; however, they reported difficulty in measuring transpulmonary pressures during the GPB maneuver (17). Extrapolating the volume-pressure relationship of Rohrer and subsequent authors (2, 10, 15, 16) above 100% VC (equivalent to 50 cmH₂O) suggests that the greater proportion of the increased mouth relaxation pressure measured here, averaging 65 (19) cmH₂O, is generated by lung recoil pressure and a lesser proportion by chest wall recoil.

The measured volume increase was closely correlated with recorded mouth relaxation pressure in the TLC_GPB state. The reporting of the volume reduction that occurs as a result of the air compression during relaxation against an obstruction is not new (2). From our subjects' results, we estimated that this air compression accounted for only a 31% reduction of our measured volume increase from TLC_PRE to the TLC_GPB state. Thus 69%, or a mean of 1.34 liters (BTPS), we estimate to be due to the volume distension of the lung. The proportional distribution between the thorax and abdomen distention is yet to be determined and is subject to blood volume redistribution (11).

Methodology limitations resulted in the volume and mouth relaxation pressure measurements being recorded independently. Both measurements were highly reproducible. This small group of athletes represents a substantial portion of the competitive breath-hold divers nationally. Their results demonstrated consistent trends in all variables measured.

Our initial hypothesis that the measured increase in TLC due to GPB resulted primarily from an increased VC with no change in RV was supported. However, gas compression made a smaller contribution to this volume increase than we predicted. Importantly, we failed to support our hypothesis that there would be no difference between baseline TLC and that acutely after ceasing GPB. The elevated TLC once ceasing GPB suggests that there has been some transient distention of the lung.

	ACKNOWLEDGMENTS

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We acknowledge Dr. Zudin Puthucheary and Extreme Spearfishing Australia for participation in this study.

	FOOTNOTES

 

Address for reprint requests and other correspondence: L. M. Seccombe, Dept. of Thoracic Medicine, Concord Repatriation General Hospital, Hospital Rd., Concord, Sydney, NSW 2139, Australia (e-mail: seccombel{at}email.cs.nsw.gov.au)

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

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This Article Abstract Full Text (PDF) Free All Versions of this Article: 101/3/799    most recent 00075.2006v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (9) Citing Articles via Google Scholar Google Scholar Articles by Seccombe, L. M. Articles by Jenkins, C. R. Search for Related Content PubMed PubMed Citation Articles by Seccombe, L. M. Articles by Jenkins, C. R.