A comparison of respiratory function in divers breathing with a mouthpiece or a full face mask.

A comparison was made of respiratory function in submersed divers breathing with either a mouthpiece or a full face mask while exposed to varying depths (15 and 190 fsw), exercise loads (0-175 W), and static lung loads (0 and -20 cmH2O). The two types of breathing equipment were designed to be identical in terms of functional dead space volume and resistance to gas flow. When compared with data from experiments utilizing a full face mask, use of a mouthpiece caused a modest fall in expired minute volume at both depths. The majority of this decline may have been the consequence of a decrease in dead space ventilation brought about by the elimination of simultaneous nose breathing and mouth breathing. Alveolar ventilation and PETCO2 were not significantly influenced by the use of a mouthpiece, regardless of depth, workload, or static lung load. With both types of breathing gear episodes of dyspnea were infrequent during experiments with a static lung load of 0 cmH2O. Therefore, if a neutral static lung load is maintained, the type of breathing gear used does not seem to be of consequence as far as dyspnea is concerned.

Simulated breath-hold diving to 20 meters: cardiac performance in humans.

Cardiac performance was assessed in six subjects breath-hold diving to 20 m in a hyperbaric chamber, while nonsubmersed or submersed in a thermoneutral environment. Cardiac index and systolic time intervals were obtained with impedance cardiography and intrathoracic pressure with an esophageal balloon. Breath holding at large lung volume (80% vital capacity) decreased cardiac index, probably by increasing intrathoracic pressure and thereby impeding venous return. During diving, cardiac index increased (compared with breath holding at the surface) by 35.1% in the nonsubmersed and by 29.5% in the submersed condition. This increase was attributed to a fall in intrathoracic pressure. Combination of the opposite effects of breath holding and diving to 20 m left cardiac performance unchanged during the dives (relative to the surface control). A larger intrathoracic blood redistribution probably explains a smaller reduction in intrathoracic pressure observed during submersed compared with nonsubmersed diving. Submersed breath-hold diving may entail a smaller risk of thoracic squeeze (lesser intrathoracic pressure drop) but a greater risk of overloading the central circulation (larger intrathoracic blood pooling) than simulated nonsubmersed diving.

Respiratory function in the upright, working diver at 6.8 ATA (190 fsw).

The influence of static lung loading on a number of respiratory parameters was investigated in subjects performing graded leg exercise in an upright posture while submerged and breathing air at ambient pressures up to 6.76 ATA. In comparison with a previous investigation of the prone posture, a lesser tendency to dyspnea was observed. Neutral and moderately positive static lung loads were associated with less dyspnea than were negative loads. Several indices of respiratory function remained relatively normal during exercise and exposure to varying static lung loads. However, there was a tendency for hypoventilation and CO2 accumulation during heavy exercise at 190 fsw; this was not strictly correlated with dyspnea or static lung load. We conclude that, if a full face mask is used, breathing gear for divers should provide a static lung load of approximately 0 to +10 cmH2O regardless of the diver's orientation in the water. When possible, divers should assume an upright posture while engaged in strenuous work.

A simple, inexpensive device for aspiration biopsy.

A simple, inexpensive aspiration device for biopsy has been described. It can be assembled quickly from readily available parts. It was primarily intended for fine needle aspiration biopsy of the thyroid gland, but it has been successfully used in our institution for computed tomography guided pulmonary biopsy as well. In addition, it can be conveniently used with a Menghini or Jamshidi needle for aspiration biopsy of other tissues. Finally, since the syringe plunger throw is adjustable, the device can be used in a clinical laboratory for the repeated sampling of identical aliquots of fluid.

A simple device for the direct measurement of mean arterial pressure and for calibration of arterial pressure monitors.

A simple, inexpensive mechanical device is described for the direct continuous measurement of mean arterial pressure. It can be assembled in minutes using a few dollars worth of sterile components commonly available in an intensive care unit. Mean arterial pressure determined in patients with this device differs by 1.6 mmHg +/- 1.1 SD from mean arterial pressure simultaneously measured by properly calibrated Hewlett-Packard electronic monitors (N = 5), a non-significant difference. Similar agreement was obtained when the device was tested using a commercial blood pressure system calibrator as the pressure source. This device also allows rapid static calibration of electronic pressure transducers across the full range of human blood pressure using a 3 ml syringe as the pressure source and an aneroid gauge, or mercury column, as the pressure standard.

Cardiac performance in humans during breath holding.

The effects on cardiac performance of high and low intrathoracic pressures induced by breath holding at large and small lung volumes have been investigated. Cardiac index and systolic time intervals were recorded from six resting subjects with impedance cardiography in both the nonimmersed and immersed condition. A thermoneutral environment (air 28 degrees C, water 35 degrees C) was used to eliminate the cold-induced circulatory component of the diving response. Cardiac performance was enhanced during immersion compared with nonimmersion, whereas it was depressed by breath holding at large lung volume. The depressed performance was apparent from the decrease in cardiac index (24.1% in the immersed and 20.9% in the nonimmersed condition) and from changes in systolic time intervals, e.g., shortening of left ventricular ejection time coupled with lengthening of preejection period. In the absence of the cold water component of the diving response, breath holding at the large lung volume used by breath-hold divers tends to reduce cardiac performance presumably by impeding venous return.

Low-frequency response characteristics of three Grass model 7 polygraphs.

A low-frequency response analysis of three Grass model 7 polygraphs was undertaken. Observed error was generally found to fall within the manufacturer's stated range of +5 to -10% of DC signal height over the frequency range of human respiration (0.1-3 Hz), but this was not the case for frequencies greater than 6 Hz under certain circumstances. The magnitude of error was seen to vary directly with frequency and indirectly with pen-deflection amplitude and paper speed. The pen-oscillograph apparatus was the predominant source of low-frequency error, and this is probably due to pen inertia and pen friction on the writing surface. Two schemes to reduce such error are presented.

Outline of medical standards for divers.

Information required for the medical examination of sport, commercial, and military divers is provided. The paper adheres to an outline format and covers the diver's medical history as well as specific points to look for in the physical and laboratory examination. Numerous disqualifying conditions are listed and they are divided into absolute contraindications and relative contraindications. Physical work capacity standards are also included as well as pressure and oxygen testing. References have been drawn from the international literature, and sources of additional medical information are provided.

Gas inertia and ventilatory measurements under pressure: methodological considerations.

A bag-in-box apparatus with a spirometer was used to measure the ventilatory minute volume in subjects exercising at air pressures up to 6.8 atm. During rest there was good agreement between minute volumes derived from the expired gas in the bag and the sum of tidal volumes from the spirometer, whereas during exercise the bag volume exceeded the spirometer volume by up to 20%. This was found to be due to the inertia of high density gas in the breathing hoses. Given sufficient flow rate the gas would continue to flow from the box to the bag following end expiration and end inspiration. The spirometer would not record this because it only responds to changes in the sum of box and bag volumes, whereas emptying the bag through a gas meter records the volume of gas actually moved. A model was constructed to investigate the phenomenon. It was concluded that many different conventional setups for respiratory measurements may be subject to this type of error. Solutions to the problem include a collapsible tube section downstream from the subject, pneumotachometers, chest-mounted magnetometers, or inductive plethysmographs.

Influence of exercise on maximal voluntary ventilation and forced expiratory flow at depth.

Four to six subjects performed maximal voluntary ventilation (MVV) and forced expirations during rest, exercise (50, 125, and 200 W), and inhalation of air and CO2 and air at rest while submerged at pressures of 1.45, 2.82, 4.64, and 6.76 atm. Maximal expiratory flow (at 40% of vital capacity) and MVV at rest decreased as exponential functions of gas density, but the decrease was less than in some earlier studies. Independent of pressure, MVV increased by about 10%-17% at the heavier work loads and expiratory flow increased by 27%-48%; the increase in expiratory flow disappeared within 2 min after exercise. Exercise increased end-tidal CO2 tension by up to 9 mmHg. Carbon dioxide inhalation increasing the end-tidal level by up to about 25 mmHg during rest had no effect on MVV and a slight to moderate effect on flow, increasing it by a maximum of 21% at 4.64 atm. The enhancing effect of exercise on MVV and expiratory flow at depth apparently was mainly due to modified autonomic nervous activity reducing pulmonary flow resistance, CO2 accumulation playing an uncertain role, and passive distension of airways playing no role.