Biomedical subjects

G M Barnas

Publications and source records attributed to G M Barnas.

At least 55 records · Page 3Linked to original sources

PubMed1992

Lung, chest wall, and total respiratory system resistances and elastances in the normal range of breathing.

We measured total respiratory system and lung and chest wall resistances (Rrs, Rl, and Rcw) and elastances (Ers, El, and Ecw) in awake, relaxed human subjects during sinusoidal volume forcing at the mouth from 0.2 to 0.6 Hz with tidal volumes (VT) of 6 to 18% VC at constant mean airway pressure. In addition, we repeated measurements with the lowest VT at a lower airway pressure and therefore at a lower mean lung volume (Vl). Rrs and Rcw decreased with increasing respiratory frequency (f) and VT, but Rl was independent of f and VT. All resistances were higher at the lower Vl. Ers and Ecw increased with increasing f and decreased with increasing VT. El increased slightly with increasing f but was not affected by VT. All elastances tended to increase at the lower Vl. We conclude that in the normal range of breathing amplitude and frequency, (1) lung properties are nearly constant if mean lung volume does not change, and (2) f and VT dependencies of total respiratory system properties are caused by the chest wall.

Adult↗

PubMed1992

Effect of tidal volume on respiratory system elastance and resistance during anesthesia and paralysis.

Recent studies have shown that the mechanical properties of the respiratory system at normal breathing frequency in awake humans depend on tidal volume. Few measurements of respiratory system properties during anesthesia have accounted for this dependence. From measurements of airway pressure, flow and esophageal pressure, we calculated elastances and resistances of the total respiratory system (Ers and Rrs), chest wall (Ecw and Rcw), and lungs (El and Rl) in supine human volunteers during quasisinusoidal volume forcing in a normal range of breathing (250 to 800 ml) at normal breathing frequency (0.2 Hz). Measurements were made (1) with subjects awake and voluntarily relaxed; (2) after isoflurane-N2O anesthesia (end-tidal isoflurane concentration 0.3 to 0.5%); and (3) after complete muscle paralysis with vecuronium. In all conditions, Ers, Ecw, El, Rrs, and Rcw decreased at 800 ml tidal volume compared with 250 ml; Rl showed a similar decrease in awake measurements only. Compared with awake measurements, each elastance tended to increase after anesthesia, but only the increase in Ers was significant. Compared with anesthesia, there was no effect of paralysis on any measurement. We conclude that (1) tidal volume dependence of respiratory system properties in the normal range of breathing occurs in the absence of muscle activity; (2) anesthesia increases Ers and (3) respiratory muscle activity appears to be inhibited by isoflurane-N2O anesthesia at end-tidal isoflurane concentration of 0.3 to 0.5% during normocapnia.

Adult↗

PubMed1992

Continuous endobronchial insufflation during internal mammary artery harvest.

Endobronchial insufflation of oxygen offers possible advantages over conventional ventilation modes in some clinical situations in which nonmovement of the chest may be desirable; however, endobronchial insufflation of oxygen has yet to be used during thoracic surgery in humans. Furthermore, the physiologic mechanisms underlying gas exchange during endobronchial insufflation of oxygen are unclear. This study assessed endobronchial insufflation of oxygen at 45 L/min in 11 patients with an open chest during internal mammary artery harvest. Cardiorespiratory function was measured at baseline during conventional mechanical ventilation and at 5-min intervals during the study period of 20-30 min. In all patients, clinically acceptable gas exchange was achieved, although PaCO2 increased from 32 +/- 3.2 to 44 +/- 7.5 mm Hg (mean +/- SD) at 5 min, but thereafter was unchanged (P greater than 0.1). Cardiac output, vascular pressures, and heart rate were unchanged, although pHa decreased. Surgical access for internal mammary artery harvesting was improved. No mucosal damage or complications occurred. During endobronchial insufflation of oxygen, efficacy of gas exchange and body weight were not correlated, but both subject height and age were correlated with high PaO2 and low PaCO2. We conclude that (a) endobronchial insufflation of oxygen can be used in patients with an open chest; (b) the efficacy of endobronchial insufflation of oxygen is probably improved by increased lung size and by collateral ventilation; and (c) cardiogenic gas mixing contributes little to gas exchange during endobronchial insufflation of oxygen.

Aged↗

PubMed1992

Changes in functional residual capacity and regional diaphragm lengths after upper abdominal surgery in anesthetized dogs.

The respiratory performance of the diaphragm may be altered by changes in mechanical or neural factors, or both, induced by upper abdominal surgery. We conducted this study to examine the effects of upper abdominal surgery on postoperative respiratory function. We studied resting lengths of four diaphragm regions, three in the costal and one in the crural diaphragm, with biplane video-roentgenography in six dogs immediately after upper abdominal surgery and up to 30 days postoperatively. Functional residual capacity was 16.7% smaller immediately after surgery compared with values obtained in the same animals after 30 days. Simultaneously measured resting lengths of each of the diaphragm regions immediately after surgery were longer, on average by 8.3%, than 30 days postoperatively. During the postoperative course, resting diaphragm lengths gradually and uniformly decreased as functional residual capacity increased. Phrenic nerve stimulation in four other dogs immediately after identical surgery resulted in large diaphragm shortening (from 42% to 55%), indicating that neither the diaphragm nor phrenic nerves were injured by the surgical manipulation. We hypothesize that respiratory dysfunction after upper abdominal surgery may be, at least in part, attributed to a decreased central drive for breathing caused by activation of the afferent limb of an inhibitory reflex owing to stretching of the diaphragm.

Abdomen↗

PubMed1991

Automated real-time data acquisition and analysis of cardiorespiratory function.

Microcomputer generation of an automated record without complexity or operator intervention is desirable in many circumstances. We developed a microcomputer system specifically designed for simplified automated collection of cardiorespiratory data in research and clinical environments. We tested the system during possible extreme clinical conditions by comparison with a patient simulator. Ranges used were heart rate of 35-182 beats per minute, systemic blood pressures of 65-147 mmHg and venous blood pressures of 14-37 mmHg, all with superimposed respiratory variation of 0-24 mmHg. We also tested multiple electrocardiographic dysrhythmias. The results showed that there were no clinically relevant differences in vascular pressures, heart rate, and other variables between computer processed and simulator values. Manually and computer recorded physiological variables were compared to simulator values and the results show that computer values were more accurate. The system was used routinely in 21 animal research experiments over a 4 month period employing a total of 270 collection periods. The file system integrity was tested and found to be satisfactory, even during power failures. Unlike other data collection systems this one (1) requires little or no operator intervention and training, (2) has been rigorously tested for accuracy using a wide variety of extreme patient conditions, (3) has had computer derived values measured against a standardized reference, (4) is reliable against external sources of computer failure, and (5) has screen and printout presentations with quick and easily understandable formats.

Computer Systems↗

PubMed1991

Respiratory system mechanical behavior in the chicken.

We evaluated whether the avian respiratory system displays the same fundamental mechanical behavior during external forcing as found in mammals. We measured airway flow and pressures in the trachea, air sacs and thoracoabdominal cavity in 4 anesthetized-paralyzed roosters during sinusoidal volume oscillations at the trachea in the normal range of euthermic breathing frequency, f(0.2 to 1.0 Hz), and tidal volume, VT (10-50 ml). From the pressure and flow waveforms, we calculated resistance (R) and elastance (E) of the total respiratory system and its major compartments (lungs, air sacs and chest wall). E of the chest wall was minimum (147 cmH2O.L-1 +/- 7 SE) at 0.2 Hz-50 ml and was consistently, slightly lower than E of the total respiratory system over the entire range studied. Both elastances showed the same dependence on f and VT, increasing slightly with increasing f and decreasing with increasing VT. R of the chest wall was maximum (35.6 cmH2O.L- 1.sec-1 +/- 2.2 SE) at 0.2 Hz-10 ml and decreased with increasing f and VT, although the VT effect diminished at the higher f. E and R of the air sacs were much smaller than those of the chest wall, but showed similar f and VT dependencies. R of the lungs, due to resistance of the airways, was minimum (6.8 cmH2O.L-1.sec-1 +/- 1.5 SE) at 0.2 Hz-10 ml and increased with both f and VT. Total respiratory R reflected R of the air sacs and chest wall at low f and R of the lungs at high f. The f and VT dependencies of E and R in the chicken were strikingly similar to those measured in various types of mammalian respiratory tissues (Stamenović et al. (1990) J. Appl. Physiol. 69: 973-988. We conclude that, despite important anatomical differences between species, avian and mammalian respiratory tissues exhibit fundamentally similar mechanical behavior.

Airway Resistance↗

PubMed1991

Efficacy of tracheal insufflation of oxygen during oleic acid-induced pulmonary edema.

STUDY OBJECTIVES: To determine whether tracheal insufflation of oxygen (TRIO) might be useful in field resuscitation of casualties with lung dysfunction. DESIGN: Physiological measurements of cardiac and respiratory function were compared before and after oleic acid lung injury. SETTING AND PARTICIPANTS: Beagles were studied in a laboratory. INTERVENTIONS: Oleic acid (0.06 mL/kg) was injected over four minutes into the central venous port of a pulmonary artery catheter. Measurements were made during 30 minutes of TRIO before and after acute lung injury. MEASUREMENTS: Hemodynamic and respiratory measurements, including intravascular pressures, heart rate, cardiac output, blood gases, respiratory system compliance, and O2 consumption were recorded during conventional mechanical ventilation and TRIO. RESULTS: Before acute lung injury, PaO2 (mean +/- SD) increased (P less than .05) from 96 +/- 7.4 (13 +/- 1.0 kPa) during conventional mechanical ventilation to 360 +/- 123 mm Hg (48 +/- 16.4 kPa) after TRIO. PaCO2 (mean +/- SD) increased (P less than .05) from 39.5 +/- 1.1 (5.3 +/- 0.1 kPa) to 102 +/- 27.4 mm Hg (13.6 +/- 3.6 kPa). Arterial and mixed venous pH values decreased in proportion to PCO2. After acute lung injury, compliance decreased. PAO2 decreased (P less than .05) to 58 +/- 8.4 mm Hg (7.7 +/- 1.1 kPa) during conventional mechanical ventilation and increased (P less than .05) to 84 +/- 19.6 mm Hg (11.2 +/- 2.6 kPa) after 30 minutes of TRIO. CONCLUSION: Despite poor gas exchange after acute lung injury, TRIO maintained adequate oxygenation and may be useful for emergency ventilation even when pulmonary edema complicates resuscitation.

Animals↗

PubMed1991

Manual resuscitators and spontaneous ventilation--an evaluation.

BACKGROUND AND METHODS: Although it is useful in certain clinical situations for manual resuscitator units to be used with spontaneously ventilating patients, there are few data regarding their performance in these settings. We measured the percent-delivered oxygen from 13 adult manual resuscitator units during simulated spontaneous ventilation in the range of respiratory frequency, tidal volume, and oxygen supply in which manual resuscitator units might be used with patients. We also measured the resistive pressure developed during simulated ventilation and at constant inspiratory flow of 50 L/min. RESULTS: Oxygen supply, tidal volume, minute ventilation, and reservoir volume all influenced percent-delivered oxygen, but the most important determinant of percent-delivered oxygen was valve design. Valves incorporating a "disc" element to prevent air entrainment from the expiratory port gave the most efficient oxygen delivery, while "duck-bill" valves did not reliably prevent air entrainment. Only two of the manual resuscitator units tested developed high resistive pressure. CONCLUSION: Reliable administration of high percent-delivered oxygen to spontaneously ventilating patients, while retaining the capability to manually ventilate them, is best achieved by a manual resuscitator unit with a valve of low resistance, incorporating a disc to prevent air entrainment. We recommend that manufacturers indicate on the product information sheet the degree (and confidence limits) to which their manual resuscitator unit presents resistance and delivers oxygen to a spontaneously ventilating subject.

Airway Resistance↗

PubMed1991

Regional chest wall impedance during nonrespiratory maneuvers.

To assess changes in total and regional chest wall properties during nonrespiratory maneuvers, we measured electromyographic activity of various chest wall muscles, esophageal pressure, and rib cage and abdominal surface displacements in six subjects before and during various static tasks. Subjects were seated at functional residual capacity, and quasi-sinusoidal forcing at the mouth (0.4 Hz, 500 ml) was imposed during the maneuver in the absence of active breathing. Magnitude of total chest wall impedance (magnitude of Zw) increased with effort during all maneuvers; changes in phase were small. Maneuvers involving primarily muscles of the neck and rib cage--holding a 10-kg weight, 10 kg of isometric tension between the arms, and isometric neck flexion--roughly doubled the magnitude of rib cage impedance (magnitude of Zrc) and, to a lesser degree, increased magnitude of diaphragm-abdomen impedance (magnitude of Zd-a). Unilateral and bilateral leg lifts, in addition to increasing magnitude of Zd-a, increased magnitude of Zrc. Passive 90 degrees rotation of the torso caused approximately 25% increases in magnitude of Zrc and magnitude of Zd-a; if the rotation was actively maintained by the trunk muscles, both regional impedances increased over 100%. Increases in magnitude of regional impedance were correlated to increases in regional electromyographic activity; changes in phase were small. Passive restriction of rib cage displacement by strapping increased magnitude of Zrc and magnitude of Zw but not magnitude of Zd-a, whereas abdominal strapping increased magnitude of Zd-a but did not affect magnitude of Zrc or magnitude of Zw.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

Proportionality between chest wall resistance and elastance.

Fredberg and Stamenovic (J. Appl. Physiol. 67: 2408-2419, 1989) demonstrated a relatively robust phenomenological relationship between resistance (R) and elastance (E) of lung tissue during external forcing. The relationship can be expressed as omega R = eta E, where omega = 2 pi times forcing frequency and eta is hysteresivity; they found eta to be remarkably invariant under a wide range of circumstances. From data gathered in previous experiments, we have tested the adequacy and utility of this phenomenological description for the chest wall (eta w) and its major compartments, the rib cage (eta rc), diaphragm-abdomen (eta d-a), and belly wall (eta bw+). For forcing frequencies and tidal volumes within the normal range of breathing, we found that eta w remained in a relatively narrow range (0.27-0.37) and that neither eta w nor the compartmental eta's changed much with frequency or tidal volume. Compared with eta w, eta rc tended to be slightly low, whereas eta d-a tended to be slightly higher than eta w. However, at higher frequencies (greater than 1 Hz) all eta's increased appreciably with frequency. During various static nonrespiratory maneuvers involving use of respiratory muscles, eta w increased up to twofold. We conclude that in the normal ranges of breathing frequency and tidal volume 1) elastic and dissipative processes within the chest wall appear to be coupled, 2) eta's of the various component parts of the chest wall are well matched, 3) respiratory muscle contraction increases the ratio of cyclic dissipative losses to energy storage, and 4) R of the relaxed chest wall can be estimated from E.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

Mechanical coupling of the rib cage, abdomen, and diaphragm through their area of apposition.

Although volumetric displacements of the chest wall are often analyzed in terms of two independent parallel pathways (rib cage and abdomen), Loring and Mead have argued that these pathways are not mechanically independent (J. Appl. Physiol. 53: 756-760, 1982). Because of its apposition with the diaphragm, the rib cage is exposed to two distinct pressure differences, one of which depends on abdominal pressure. Using the analysis of Loring and Mead as a point of departure, we developed a complementary analysis in which mechanical coupling of the rib cage, abdomen, and diaphragm is modeled by a linear translational transformer. This model has the advantage that it possesses a precise electrical analogue. Pressure differences and compartmental displacements are related by the transformation ratio (n), which is the mechanical advantage of abdominal over pleural pressure changes in displacing the rib cage. In the limiting case of very high lung volume, n----0 and the pathways uncouple. In the limit of very small lung volume, n----infinity and the pathways remain coupled; both rib cage and abdomen are driven by abdominal pressure alone, in accord with the Goldman-Mead hypothesis. A good fit was obtained between the model and the previously reported data for the human chest wall from 0.5 to 4 Hz (J. Appl. Physiol. 66:350-359, 1989). The model was then used to estimate rib cage, diaphragm, and abdominal elastance, resistance, and inertance. The abdomen was a high-elastance high-inertance highly damped compartment, and the rib cage a low-elastance low-inertance more lightly damped compartment. Our estimate that n = 1.9 is consistent with the findings of Loring and Mead and suggests substantial pathway coupling.

Abdomen↗

PubMed1991

Dependencies of respiratory system resistance and elastance on amplitude and frequency in the normal range of breathing.

We calculated respiratory system resistance (Rrs) and elastance (Ers) from pressure and flow at the mouth in six seated subjects relaxed at FRC (cheeks tightly compressed) during sinusoidal volume forcing (250, 500, and 750 ml) at 0.2, 0.4, and 0.6 Hz. Dependencies of Rrs and Ers on frequency and tidal volume were generally the same in each subject; Rrs tended to decrease with frequency and tidal volume, whereas Ers tended to increase with frequency and decrease with tidal volume. Multiple linear regression of combined data indicated that the frequency and tidal volume effects on Rrs and Ers were significant (p less than 0.05), and that the effects on Rrs decreased at higher flows. Average Rrs was highest (4.43 cm H2O/L/s +/- 0.21 SE) at 0.2 Hz-250 ml, and lowest (3.07 cm H2O/L/s +/- 0.37) at 0.6 Hz-750 ml. Average Ers was highest (12.1 cm H2O/L +/- 1.1) at 0.6 Hz-250 ml, and lowest (7.1 cm H2O/L +/- 0.6) at 0.2 Hz-750 ml. We conclude that frequency and tidal volume dependencies in Rrs and Ers in the normal range of breathing should be considered when interpreting measurements of respiratory system impedance or developing models to describe the mechanical behavior of the respiratory system.

Airway Resistance↗

PubMed1990

Shivering and cardiorespiratory responses during normocapnic hypoxia in the pigeon.

To study the inhibitory effect of hypoxia on the cold defense mechanism, pigeons were exposed at low ambient temperature (5 degrees C) to various inhaled gas mixtures: normoxia [0.21 fractional concentration of O2 (FIO2)], hypoxia (0.07 FIO2), and normocapnic hypoxia (0.07 FIO2 + 0.045 FICO2). Electromyographic (EMG) activity indicative of shivering thermogenesis was inhibited during hypoxia, and body temperature (Tre) fell by 0.09 degrees C/min. Respiratory frequency (f) and minute ventilation (VE) increased by 143 and 135%, respectively, compared with normoxia, but tidal volume (VT) was not changed. PO2, PCO2, and O2 contents in the arterial and mixed venous blood were decreased and pH was enhanced. During normocapnic hypoxia, shivering EMG was present at approximately 50% of the normoxic intensity; Tre fell by only 0.04 degrees C/min. Arterial and mixed venous PCO2 and pH were the same as during normoxia, but VE increased by 430% because of twofold increases in both f and VT. During normocapnic hypoxia, arterial PO2 and O2 content were higher than during hypoxia alone. We conclude that the persistence of shivering during normocapnic hypoxia is due to maintenance of critical levels of arterial PO2 and O2 content.

Animals↗

PubMed1990

Total and local impedances of the chest wall up to 10 Hz.

To understand how bical mechanical chest wall (CW) properties are related to those of the CW as a whole, we measured esophageal and gastric pressures, CW volume changes (measured with a head-out body plethysmograph), and anteroposterior and transverse CW diameter changes (measured with magnetometers attached to the surface) during sinusoidal forcing at the mouth (2.5% vital capacity, 0.5-10 Hz) in four healthy subjects. Total CW resistance decreased sharply as frequency rose to 3-4 Hz and remained relatively constant at higher frequencies. Total CW reactance became less negative with increasing frequency but showed no tendency to change sign. Above 2 Hz, diameters measured at different locations changed asynchronously between and within the rib cage and abdomen. "Local pathway impedances" (ratios of esophageal or gastric pressure to a rate of diameter change) showed frequency dependence similar to that of the total CW less than 3 Hz. Local pathway impedances increased during contraction of respiratory muscles acting on the pathway. We conclude that 1) total CW behavior is mainly a reflection of its individual local properties at less than or equal to 3 Hz, 2) local impedances within the rib cage or within the abdomen can change independently in some situations, and 3) asynchronies that develop within the CW during forcing greater than 3 Hz suggest that two compartments may be insufficient to describe CW properties from impedance measurements.

Abdominal Muscles↗

PubMed1990

Abdominal pressure transmission in humans during slow breathing maneuvers.

Pressure transmission within the abdomen was studied in four subjects standing and supine, breathing slowly and performing slow breathing maneuvers. Pressures were measured in the stomach and rectum with air-containing balloon-catheter systems Pga(air) and Prec and in the stomach with a water-filled catheter system Pga(liq). Changes in Pga(air), Pga(liq), and Prec were nearly in phase and linearly related. The changes in Pga(liq) and Prec were nearly equal in all maneuvers, whereas the changes in Pga(air) were systematically greater than those of Pga(liq) and Prec during quiet breathing and relaxation maneuvers in the upright position. During expulsive maneuvers in either posture the abdominal shape and stomach position were relatively constant, and the changes in Pga(air) were nearly equal to those of Pga(liq) and Prec. Discrepancies between changes in Pga(air) and the other pressures were consistent with presumed changes in the height of the gastric air bubble. We conclude that abdominal pressure in humans is essentially hydrostatic during quiet breathing and slow breathing maneuvers.

Abdomen↗

PubMed1990

Effects of cardiac oscillations and lung volume on acinar gas mixing during apnea.

We evaluated the importance of cardiogenic gas mixing in the acini of 13 dogs during 2 min of apnea. 133Xe (1-2 mCi in 4 ml of saline) was injected into an alveolar region through an occluded pulmonary artery branch, and washout was measured by gamma scintillation scanning during continued occlusion or with blood flow reinstated. The monoexponential rate constant for Xe washout (XeW) was -0.4 +/- 0.08 (SE) min-1 at functional residual capacity (FRC) with no blood flow in the injected region. It decreased by more than half at lung volumes 500 ml above and 392 ml below FRC. With intact pulmonary blood flow, XeW was -1.0 +/- 0.08 (SE) min-1 at FRC, and it increased with decreasing lung volume. However, if calculated Xe uptake by the blood was subtracted from the XeW measured with blood flow intact, resulting values at FRC and at FRC + 500 ml were not different from XeW with no blood flow. Reasonable calculation of Xe blood uptake at 392 ml below FRC was not possible because airway closure, increased shunt, and other factors affect XeW. After death, no significant XeW could be measured, which suggests that XeW caused by molecular diffusion was small. We conclude that 1) the effect of heart motion on the lung parenchyma increases acinar gas mixing during apnea, 2) this effect diminishes above or below FRC, and 3) there is probably no direct effect of pulmonary vascular pulsatility on acinar gas mixing.

Animals↗

PubMed1990

Viscoplasticity of respiratory tissues.

Low-frequency mechanical behavior of various respiratory tissues shows certain similarities. In this study we test the hypothesis that rate-independent plastic processes along with rate-dependent viscoelastic processes are responsible. We considered oscillatory responses of several respiratory tissues measured over prescribed ranges of frequency (up to 6 Hz) and amplitude of forcing. These included the excised cat lung, the human chest wall in vivo, and two components of the chest wall: the excised dog rib cage and the excised rabbit abdominal viscera; some data were previously reported and some are new. We analyzed these data using the viscoplastic model of Hildebrandt (J. Appl. Physiol. 28: 365-372, 1970). It consists of three compartments: a plastoelastic compartment mechanically in parallel with a viscoelastic compartment, both in series with a lumped inertia. We fitted oscillatory data of the above respiratory tissues to the model by a least-squares technique. The fit was qualitatively consistent with the observations and exhibited moderately good to very good quantitative correspondence. As an independent verification of this approach, we obtained the stress relaxation after a step-volume change. Based on the oscillatory response of cat lungs, the calculated stress relaxation function was found to be generally consistent with corresponding observations. This study indicates that both plasticity and viscoelasticity appear to be important determinants of mechanical behavior of respiratory tissues at low frequencies and that inertial effects are negligible.

Animals↗

PubMed1990

Low-flow endobronchial insufflation with air for 2 hours of apnea provides ventilation adequate for survival.

We tested the efficacy of low-flow endobronchial insufflation (EI) with air, as it may be useful in emergency situations in which positive-pressure mechanical ventilation is not possible. The only equipment required is a source of compressed air with flow controller and a specially designed insufflation catheter. The insufflation catheter has forked ends that can be positioned blindly in the mainstem bronchi. In six anesthetized, apneic dogs averaging 9.6 kg, we determined that the average air flow needed to maintain PaO2 above 45 mm Hg and PaCO2 below 65 mm Hg after 30 min was 2.5 L/min. At these flow rates, all dogs survived 2 h of endobronchial insufflation with no neurologic dysfunction. The small internal diameters (0.8 mm) of the catheter ends increase gas exit velocity and allow for adequate oxygenation and CO2 removal at low flow rates. Endobronchial insufflation could also be employed with cricothyroidotomy and a compressor for emergency situations in the field involving mass casualties, where oxygen supplies and equipment are limited.

Animals↗