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.     

Effects of immersion and static lung loading on submerged exercise at depth

The effects of static lung loading in the range +20 cmH2O to -20 cmH2O was investigated in 3 male subjects breathing air during submerged exercise in the prone position at pressures ranging from 1.45 ATA to 6.76 ATA. Both maximal and submaximal exercise was performed and dry controls were done at 1.45 ATA. A low-resistance bag-in-a-box breathing apparatus (less than 1.25 cmH2O/liter/s at 8 g/liter density) was used. Static lung loading had little effect on maximal or submaximal VO2, VCO2, VE, heart rate, or end-tidal PCO2, while increased breathing gas density did affect these parameters to a larger extent. Imersion per se reduced the VE at a given level of VO2 and increased both the VT and VA at a given VE. Increasingly positive static lung load increased VC and ERV both during rest and exercise. Exercise-induced dyspnea was experienced and scored. At submaximal VO2 levels up to 2.5 liter/min this dyspnea did not limit exercise at any depth, but during maximal exertion at 6.76 ATA (VO2 from 3.45--3.77 liter/min), dyspnea became work limiting in several cases. Static load had a marked effect on dyspnea and a load of +10 cmH2O produced the least dyspnea, enabling all subjects to perform maximal exertions for 5 min at 6.76 ATA. The 15-s MVV was performed at all depths and static loads and neither it nor the VE/MVV ratio correlated with the degree of dyspnea.     

Respiratory function during simulated wet dives

This presentation focuses on the effects of static lung loading (SLL) on diver performance. It is noted that SLL may arise from depth differences between the diver's chest and his breathing gear. Studies are reviewed in which subjects undergoing wet, simulated dives in a pressure chamber were exposed to SLL ranging from 14.7 to -14.7 mmHg (+20 to -20 cmH2O) while breathing air at depths down to 58 m (190 ft). The subjects, assuming a prone or an upright position, performed leg exercise on an underwater bicycle ergometer. Various measurements of respiratory function were made. By applying a scoring scale for dyspnea it was found that in addition to being more pronounced as exercise and depth (gas density) increased, the dyspnea was most pronounced with negative SLL. Positive SLL alleviated the dyspnea. The dyspnea also tended to be more pronounced in the prone than in the upright posture. It was speculated that this may have been partly due to more of a compression effect on the extra thoracic airways by water pressure in the former than in the latter posture. There were no marked differences in gas exchange and end-tidal gas concentrations with different static lung loads, and it was hypothesized that differences in respiratory muscular strain may have accounted for the differences in dyspnea with different SLLs. That the dyspnea was inspiratory in nature would agree with the observation that positive SLL aiding inspiration would be perceived as beneficial. A breathing apparatus design that counteracts undesirable SLL is reviewed.     

Physiologically and subjectively acceptable breathing resistance in divers' breathing gear.

To determine acceptable levels of breathing resistance in divers' gear, 6 subjects were exposed to varying levels of breathing resistance under demanding and realistic conditions. The immersed air-breathing subjects exercised in the prone position at 60% of their maximum oxygen uptake for 25 min in a hyperbaric chamber at 1.45 and 6.8 atm abs (145 and 690 kPa, 4.5 and 57 msw, 15 and 190 fsw). The breathing resistance ranged from minimal to 8-12 cmH2O (0.8-1.2 kPa).liter-1.s at flow rates of 2-3 liter/s. The higher resistance levels interfered with the respiration in terms of end-tidal PCO2 and dyspnea scores. There were considerable individual differences, and changes in one parameter were typically not paralleled by changes in the other. None of maximal voluntary ventilation, forced expiratory volume, expiratory reserve volume, vital capacities, or oxygen uptake was influenced by resistance. We set the maximum allowable end-tidal PCO2 at 60 mmHg and maximum dyspnea score at 1.0 on a scale from 0 (none) to 3 (severe). Based on these criteria we concluded that the external work of breathing should not exceed 1.5-2.0 J/liter in the ventilation range 30 to 75 liter/min BTPS.     

Noninvasive measurement of respirator effect at rest and during exercise

Ventilation and respiratory timing during rest and exercise were measured in normal volunteers by pneumotachograph and by respiratory inductive plethysmography (RIP) to determine if RIP is accurate and to determine if the usual methods of ventilation measurement during respirator research lead to artifacts. Data were collected with a mouthpiece, a sham mouthpiece, and no mouthpiece. A dead space and inspiratory resistance load similar to respirators were employed also. The study showed that no significant artifact is produced, particularly during exercise, by measurements using a mouthpiece. RIP is sufficiently accurate and precise for use in unobtrusively measuring ventilation during respirator studies when traditional methods cannot be used.     

Static lung load and posture effects on pulmonary mechanics and comfort in underwater exercise.

Static lung load (SLL), or transrespiratory pressure gradient, imposed by underwater breathing apparatus can affect breathing comfort and mechanics, especially during exertion. We examined the effects of body position and SLL on two factors known to affect or limit exertion: a) tidal flow-volume limitation, i.e., the percentage of the tidal volume that meets the boundary of the maximum expiratory flow-volume curve; and b) breathing discomfort. Eight healthy male scuba divers (28 +/- 4 yr) performed cycle ergometry to exhaustion during immersion in each of four combinations of body position and SLL: upright, prone, +10 cmH2O, -10 cmH2O. SLL was referenced to the sternal notch. Tidal flow-volume limitation was significantly greater with the negative SLL (P less than 0.05). In the prone position, higher expiratory flows were achieved (P less than 0.01) and flow limitation was not significantly increased. Respiratory discomfort was quantified with a psychophysical rating scale and increased significantly as exercise intensity increased (P less than 0.01). No effect of posture or SLL on discomfort was found. We conclude that, although respiratory comfort is unaffected, positive static lung loading and the prone body position minimize adverse changes in respiratory mechanics during exercise in immersion.     

盐酸氨溴索气道湿化对婴幼儿重症肺炎机械通气时呼吸力学的影响

目的 观察机械通气时用盐酸氨溴索气道湿化对婴幼儿重症肺炎呼吸力学的影响.方法 选取符合婴幼儿重症肺炎诊断标准并需机械通气治疗的65例婴幼儿,按随机数字表法分为试验组33例和对照组32例.试验组用盐酸氨溴索气道湿化,对照组用0.9％氯化钠,每次2 ml气管内滴入,然后接球囊加压给氧30 s,再接呼吸机通气,湿化后5 min彻底吸痰,24 h后观察治疗前后呼吸力学指标的变化：平均气道阻力、肺顺应性、呼吸功、气道平台压.比较两组治疗前后呼吸力学指标改变.结果 机械通气治疗24 h后,试验组呼吸力学指标较对照组明显改善[平均气道阻力分别为（0.68±0.04） cmH2O/（L·s）和（0.57±0.05） cmH2O/（L·s）,1 cmH2O=0.098 kPa,肺顺应性分别为（3.17±0.81） ml/kPa和（2.56±0.69）ml/kPa,呼吸功分别为（0.54±0.08） J/L和（0.41±0.06） J/L,气道平台压分别为（2.23±0.58） cmH2O和（2.12±0.63） cmH2O],差异有统计学意义（P＜0.05）;试验组较对照组机械通气时间明显缩短,分别为（64.08±13.92）h和（79.57±19.64）h,差异有统计学意义（P＜0.05）.结论 机械通气时给予盐酸氨溴索气道湿化,能够改善婴幼儿重症肺炎呼吸力学指标,有效治疗重症肺炎,减少气道阻力,改善肺泡通气,缩短机械通气时间.     

Determinants of pattern of breathing during respirator use

The relationship between the pattern of breathing in response to respirator-type loads and an individual's psychophysiologic sensitivity to loads (load scaling sensitivity, LSS) was investigated in the study of 11 normal volunteers. LSS was measured by having the subjects numerically rate a series of resistors; Steven's Psychophysical Law was used to evaluate sensitivity as the slope relating log (sensation) to log (stimulus). Peak pressure and actual added resistance were the stimuli. Inspiratory time, peak pressure, duty cycle, and tidal volume were inversely related to independently measured LSS during exercise and with a respiratory-type dead space and inspiratory resistance load. Because the need for changes in respiratory timing is a major adaptation in respirator use, it suggests that workers who are very sensitive to loads may have limited ability to adapt to respirator use.     

两种肺保护通气模式在重症创伤性湿肺通气策略中的比较

目的 比较两种肺保护通气模式在重症创伤性湿肺时施行肺保护通气策略中的临床意义.方法 将92例重症创伤性湿肺患者按随机数字表法分为适应性支持通气（ASV）组和压力型同步间歇指令通气（P-SIMV）＋压力支持通气（PSV）组,每组46例,比较两组患者机械通气后30 min的心率、平均动脉压（MAP）、pH值、动脉血氧分压（PaO2）、动脉血二氧化碳分压（PaC O2）、每分钟通气量、潮气量、总呼吸频率、气道峰压、平均气道压、气道闭合内压、肺顺应性.结果 机械通气后30 min,两组患者心率、MAP、pH值、PaO2、PaCO2、平均气道压、气道峰压、气道闭合内压比较差异均无统计学意义（P＞0.05）,但ASV组潮气量、每分钟通气量、总呼吸频率、肺顺应性均较P-SIMV＋PSV组明显改善[（692.6±38.6） ml比（558.5±25.6） ml、（8.9±1.7）L比（7.8±1.6）L、（16.3±3.3）次/min比（21.3±3.2）次/min、（42.15±5.28） ml/cmH2O（1 cmH2O=0.098 kPa）比（39.15±5.47） ml/cmH2O],差异均有统计学意义（P＜0.01或＜0.05）.结论 对于重症创伤性湿肺患者在施行肺保护通气策略时,ASV可根据患者的呼吸力学状况自动调整吸气压力支持水平,提高潮气量、增加肺顺应性、降低呼吸频率,而对血流动力学和生命体征无明显影响.     

The use of inductive plethysmography in the study of the ventilatory effects of respirator wear

The authors recently developed an ambulatory system, in which a self-contained respiratory inductive plethysmograph (RIP) was used, to measure noninvasively the volume and time components of breathing. Since it does not use nasal or oral devices, such a system is particularly suitable for use in studying the effects of respiratory protective masks on respiratory parameters. In order to validate this portable system, 22 healthy subjects were exercised on a treadmill; RIP and pneumotachographic minute ventilation measurements were compared. A short, graded submaximal exercise protocol was run 3 times by each subject under each of the following conditions: no oral mouthpiece; oral mouthpiece with pneumotachograph; and wearing an industrial protective mask (half facepiece, twin cartridge). Chest and abdominal RIP signals, a time signal and either a pneumotachograph or heart-rate signal were recorded on a small cassette recorder worn at the belt. The data tapes were later edited and analyzed by computer. Data from 5 subjects were excluded because of equipment malfunction. The average error in RIP-measured ventilation compared to values simultaneously measured by a pneumotachograph in the 17 remaining subjects over all exercise levels was -3.16%. Marked variability (SD = 11.26%), however, was found in individuals at different exercise levels and especially between subjects. Use of a respirator was associated with a decreased respiratory frequency, an increased tidal volume and minute ventilation, and an unchanged heart rate. At present, the portable RIP system has substantial variability that limits its ability to measure ventilation accurately.     

单肺通气不同水平呼气末正压对胸腔镜肺大疱切除术患者血气分析及血流动力学的影响

目的 探讨单肺通气时应用不同水平的呼气末正压（PEEP）对胸腔镜肺大疱切除术患者术中血气分析及血流动力学的影响.方法 将78例行胸腔镜肺大疱切除术患者按随机数字表法分为三组,每组26例：Ⅰ组双肺通气后仅给予单肺间歇正压通气（IPPV）,Ⅱ组双肺通气后给予单肺IPPV加PEEP5 cmH2O（1 cmH2O=0.098 kPa）,Ⅲ组双肺通气后给予单肺IPPV加PEEP 10 cmH2O.记录并比较三组平卧位双肺通气、侧卧位双肺通气、单肺通气10和30 min的血气分析和血流动力学.结果 三组患者脉搏血氧饱和度均维持在0.99～ 1.00.三组各时间点pH值、剩余碱、动脉血二氧化碳分压（PaCO2）、HCO3-比较差异均无统计学意义（P＞0.05）.Ⅱ、Ⅲ组单肺通气10,30 min动脉血氧分压（PaO2）明显高于Ⅰ组[（336.2±113.2）,（348.5±109.7） mmHg（1mmHg=0.133 kPa）比（285.0±103.5） mmHg,（357.6±104.0）,（358.9±103.2） mmHg比（276.0±107.2） mmHg],差异有统计学意义（P＜0.05）,但均在正常范围内,Ⅱ组和Ⅲ组比较差异无统计学意义（P＞0.05）.三组各时间点心率、平均动脉压、左心室射血时间、体循环血管阻力比较差异均无统计学意义（P＞0.05）.Ⅱ组和Ⅲ组单肺通气10,30 min每搏输出量、心输出量明显低于本组平卧位双肺通气、侧卧位双肺通气及Ⅰ组同期,差异均有统计学意义（P＜0.05）,但均在正常范围内,Ⅱ组和Ⅲ组比较差异无统计学意义（P＞0.05）.结论 双肺通气后给予单肺IPPV加PEEP 5 cmH2O在胸腔镜肺大疱切除术中能维持满意的PaO2和PaCO2,血流动力学变化不明显;但PEEP 5 cmH2O较仅IPPV能进一步提高PaO2,而PEEP 10 cmH2O却没有进一步提高PaO2.     

Comparison of indirect calorimetric measurements of resting energy expenditure with a ventilated hood, face mask, and mouthpiece

This study compared three techniques for indirect calorimetric measurement of resting energy expenditure: ventilated canopy, face mask, mouthpiece plus noseclips. A total of 18 healthy men and women underwent all three measurement techniques in three consecutive 20-min measurement periods in a Latin square design. No significant effects were found for either period or method with respect to oxygen consumption, respiratory exchange ratio, and caloric expenditure. Oxygen consumption was (mean +/- SD) 250 +/- 45, 251 +/- 47, and 254 +/- 49 mL/min for hood, mask, and mouthpiece, respectively (ns). The respiratory exchange ratio was lower for the hood (0.809 +/- 0.051) than mask (0.837 +/- 0.043) and mouthpiece (0.847 +/- 0.045) but this difference was not statistically significant (p = 0.07). Calculated caloric expenditure was 1.20 +/- 0.22, 1.21 +/- 0.22, and 1.23 +/- 0.23 kcal/min for hood, mask, and mouthpiece, respectively (ns). Thus, in healthy individuals similar results are obtained by the three methods and the face mask and mouthpiece are acceptable alternatives to the ventilated hood for estimation of resting energy expenditure.     

Phosgene: a practitioner's viewpoint

Clinical experience with five patients exposed to phosgene is described. The treatment of phosgene poisoning was focused upon the presenting problem, pulmonary edema. Arterial hypoxemia was treated with a face mask with 10 cm CPAP with the FiO2 adjusted as needed or with a volume ventilator with controlled ventilation. Ventilation was controlled to reduce the work of breathing. Metabolic acidosis was treated with NaCHO3 to produce a normal pH. A vigorous program of diuresis was used to treat the pulmonary edema. Lasix was administered to produce a negative fluid balance while maintaining a good urinary output. The negative fluid balance correlated well with reduced oxygen requirements.     

CO2 retention with minimal symptoms but severe dysfunction during wet simulated dives to 6.8 atm abs

During wet dives in a hyperbaric chamber to 6.8 atm abs (690 kPa), air breathing subjects were experimentally exposed to external breathing resistance. Two of them were, unbeknownst to themselves, severely incapacitated. In the first incident the subject had been exercising for 25 min (end-tidal PCO2 60-65 mmHg, 7.3-8.0 kPa) when the breathing resistance was rapidly increased from low to very high (requiring pressure swings of 80 cmH2O, 8 kPa, peak to peak). He functioned normally (end-tidal PCO2 72 mmHg, 9.6 kPa) for about 100 s but 20 s later he was confused and irrational. After being extracted from the water (end-tidal PCO2 above 90 mmHg, 12 kPa), he lost consciousness for about 60 s. In the second incident the subject was exercising and breathing against a high resistance (pressure swings of 50-55 cmH2O, 5.0-5.6 kPa). His end-tidal PCO2 was high (65-68 mmHg, 8.7-9.3 kPa) throughout the exercise period, and after 24 min he reported mild dyspnea. A few seconds later he became confused. In other experiments both subjects voluntarily terminated experiments when the breathing resistance became overwhelming. These 2 subjects generally had high end-tidal PCO2 levels, but 1 other subject with end-tidal PCO2 levels in the same range never experienced any problems. These incidents indicate that severe hypercapnia does not necessarily correlate with dyspnea and that severe disturbances in mental function due to hypercapnia can develop suddenly when high breathing resistance is encountered in diving.     

Pulmonary atelectasis formation during diving with closed-circuit oxygen breathing apparatus

The physiological effects of diving with two types of closed-circuit oxygen breathing apparatus were investigated in 4 divers. In one apparatus the breathing bag was mounted on the dorsum and in the other on the chest, inducing -2 kPa and +1 to +2 kPa static lung load in the prone position, respectively. The back-mounted bag caused an unfavorable swimming position, with increased heart rate, breathing rate, and rating of perceived exertion (RPE) for work load. The greater internal and external work of breathing (the latter judged from the higher RPE for breathing resistance) probably contributed to a higher RPE for discomfort with the back-mounted bag. Three divers showed great reduction in vital capacity (VC) (0.8 to 1.9 liters) and developed coughing attacks after dives with this apparatus; these results were interpreted as possible indications of atelectasis formation. The 4th diver showed slight reduction in VC with both types of bag, possibly because the changes in static lung loads did not influence the airway closure in this man.     

Effects of Sarcopenia on Ventilatory Behavior and the Multidimensional Nature of Dyspnea in Patients With Chronic Obstructive Pulmonary Disease

ObjectivesThis study tested the hypothesis that sarcopenia, a common extrapulmonary feature of chronic obstructive pulmonary disease (COPD), can affect ventilatory behavior, and worsen the multidimensional nature of dyspnea in patients with COPD.DesignCross-sectional survey study.Settingand Participants: Stable outpatients with COPD encountered in general practice and respiratory clinic.MethodSarcopenia was diagnosed according to an appendicular skeletal muscle mass index based on measurements of electrical impedance and handgrip strength. Exertional dyspnea was tested using a 3-minute Step Test and a 6-minute Walk Test. The dimensions of dyspnea were assessed by a multidimensional dyspnea profile.ResultsOf 60 stable patients with COPD, 16 met the criteria for sarcopenia. During the 3-minute Step Test, minute ventilation as a proportion of exercise time, tidal volume as a proportion of inspiratory capacity, the change in inspiratory capacity, and ventilation as a proportion of maximal voluntary ventilation did not differ between patients with and without sarcopenia. Patients with sarcopenia exhibited lower evolution of tidal volume, higher evolution of respiratory frequency versus ventilation and breathing discomfort on the 3-minute Step Test, as well as increased physical breathing effort on the 6-minute Walk Test, compared with those without sarcopenia. In a multivariable model adjusted using inverse probability weighting, sarcopenia was independently associated with breathing discomfort during the 3-minute Step Test and physical breathing effort during the 6-minute Walk Test.Conclusions and ImplicationsSarcopenia may be associated with shallow breathing and diverse sensory and affective components of exertional dyspnea in patients with COPD. The study indicates that improvement of the rapid breathing pattern may offer unique ways to alleviate dyspnea in older patients with COPD and sarcopenia.     

The head dome: a simplified method for human exposures to inhaled air pollutants

Acute controlled exposures of human subjects to air pollutants are customarily carried out with whole-body chambers, masks, or mouthpieces. The use of these methods may be limited by cost or technical considerations. To permit a study involving a highly unstable pollutant, artificial acid fog, administered to subjects during natural breathing, a head-only exposure chamber, called a head dome, was developed. It consists of a transparent cylinder with a neck seal which fits over the subject's head and rests lightly on his shoulders. The head dome does not constrain the upper airways or impede exercise on a bicycle ergometer. Ventilation can be monitored accurately and unobtrusively with a pneumotachograph at the exhaust port of the dome. A thermocouple may be used to monitor the onset and persistence of oronasal breathing. For short-term exposures to unstable or reactive pollutants lasting up to several hours, the head dome is an effective alternative to a whole-body chamber and probably superior to a face mask or mouthpiece.     

Alterations in physiological and perceptual variables during exhaustive endurance work while wearing a pressure-demand respirator

The purpose of this investigation was to describe the time course of changes in physiological and perceptual variables during exhaustive endurance work with and without an air-supplied, full-facepiece, pressure-demand respirator. Thirty-eight healthy subjects (24 to 51 years of age) volunteered for this study. Treadmill speed was set at 5.5 kph (3.4 mph) and elevation was set at a level calculated to elicit 70% of a previously determined maximal aerobic capacity (VO2max). Subjects continued at this rate to exhaustion. Despite a constant work rate, VO2 and %VO2max increased during exercise and were significantly greater with the respirator (34.4 +/- 1.1 mL/kg.min; 84% VO2max) than without the respirator (31.9 +/- 1.1 mL/kg.min; 76% VO2max) at the "final" measurement point prior to termination of exercise by each subject. The final values for ventilation volume (VE) also were significantly greater with the respirator (89.2 +/- 3.4 L/min) than without (73.4 +/- 3.7 L/min). At the conclusion of the endurance walk, dyspnea index (VE/MMV.25) remained well below maximal values (with = 58.6 +/- 2%; without = 44.6 +/- 2%; p less than 0.001). Also, at the final period, no significant differences occurred in the subjects' perceptual ratings of work of breathing, yet work performance time was significantly reduced (p less than 0.0001) from 69.1 +/- 4.4 min (without) to 55.6 +/- 3.8 min (with). A significantly greater swing in peak pressure (maximum pressure measured within the facepiece of respirator), however, from inspired (PPi) to expired (PPe) occurred with the respirator (13.42 cmH2O) than without the respirator (9.25 cmH2O).(ABSTRACT TRUNCATED AT 250 WORDS)     

小儿重症喘息性疾病机械通气时压力-容积曲线的应用

目的 探讨小儿重症喘息性疾病机械通气治疗时是否能够使用呼气末正压(PEEP),以及如何确定最佳PEEP的简捷方法.方法 采取自身对照法,记录儿科重症监护室(PICU)中23例需要机械通气的重症喘息性疾病患儿的准静态压力-容积(P-V)曲线,确定P-V曲线上低位转折点(LIP),将PEEP分别设定在准静态曲线的0 cm H2O、LIP、LIP+2 cm H2O(1 cm H2O=0.098 kPa)三组,以相同的潮气量和吸入氧浓度(FiO2)分别给予定容机械通气,各水平PEEP维持30 min后监测肺呼吸力学和血流动力学参数、动脉血气改变.结果 23例重症喘息性疾病患儿的准静态LIP为(2.70±2.00) cm H2O.当PEEP为LIP+2 cm H2O时,动脉血氧分压(PaO2 )/FiO2及肺顺应性均显著提高(P＜0.01),动态肺顺应性最高,吸气峰压为(22.30±3.00) cm H2O,平均气道压为(14.11±1.01)cm H2O,且对平均动脉压及心率无明显影响.与PEEP为0 cm H2O相比较,动脉血二氧化碳分压(PaCO2)无明显区别.结论 小儿重症喘息性疾病时,应用PEEP是安全的,选择准静态P-V曲线的LIP+2 cm H2O作为PEEP水平时可获较佳治疗效果,且不会加大CO2的潴留,对血流动力学也无明显影响.