Improvement after lung volume reduction surgery: a role for inspiratory muscle adaptation

In severe emphysema, lung volume reduction surgery (LVRS) can improve lung function and exercise tolerance. The maximal changes of forced expiratory volume in 1s (FEV(1)) and lung volume occur early after surgery, whereas maximal improvement of exercise tolerance occurs later. We tested the hypothesis that secondary adaptation of inspiratory muscles could explain this delayed clinical improvement. In that purpose, we evaluated nine consecutive patients before LVRS and up to 9 months post-operatively. Six weeks after LVRS, we observed an increase in FEV(1) and 6 min walk distance (6MWD). The gain in sniff nasal inspiratory pressure (SNIP) was inversely proportional to lung volume loss. Values of FEV(1) and lung volume were maintained throughout follow-up whereas SNIP values significantly increased from 6 weeks to 6 months post-LVRS. In the meantime, we observed an increase in 6MWD correlated with the SNIP increase. This suggests that in patients undergoing LVRS, early improvement of SNIP is proportional to decrease in lung volume whereas the further delayed improvement may be due, at least in part, to adaptation of the inspiratory muscles.     

Quantification of single-breath underestimation of lung volume in emphysema

The extent to which a single breath measurement represents available gas dilutional as well as compressible thoracic volume in emphysema patients has not been quantified. We therefore measured single breath (TLC_SB) and rebreathe helium dilution (TLC_RB), and plethysmographic lung volume (TLC_pleth), in fifty-five outpatients with clinical and radiographic emphysema, and in twenty-one normal controls. Among emphysema patients, TLC_SB increasingly underestimated both TLC_pleth and TLC_RB as FEV₁% predicted decreased (p for interaction = 0.001 for both) by a mean of 1.7 l for TLC_RB (p < 0.001) and 2.2 l for TLC_pleth (p < 0.001). In contrast, TLC_RB underestimated TLC_pleth by a mean of 0.5 l (p < 0.001) regardless of FEV1% (p for interaction = 0.25). TLC_SB, TLC_RB, and TLC_pleth showed strong agreement among normal subjects. We conclude that TLC_SB underestimates available gas dilutional and compressible lung volume as physiologic emphysema severity increases. In contrast, TLC_RB and TLC_pleth show closer agreement which is unaffected by physiologic emphysema severity.     

手工缝合肺残面施行肺减容手术治疗重度肺气肿

目的 探讨手工缝合肺残面方法肺减客手术治疗重度慢性阻塞性肺气肿的疗效。方法 本组肺减容手术20例，其中双侧肺减容6例，单侧肺减容14倒。切口的选择依据手术切除靶区的位置，其中平卧位正中切口、双侧LVRS1例，侧卧住后外侧开胸LVRS14侧，前外侧开胸LVRS11侧。术前及术后6月查肺功能（FEV1，TLC，RV）、动脉血气分析、6分钟步行距离进行对比。结果 本组无手术死亡，患者术后肺功能指标比术前有明显改善（P〈0．05），动脉血氧分压术后比术前明显提高（P〈0．05），二氧化碳分压术后比术前明显降低（P〈0．05）；呼吸困难指数再分级，15例术前3级中6例转为1级，9例转为2级；5例4级中1例转为3级，3例转为2级，1例转为1级。结论 重度肺气肿病人行肺减容手术，能改善患者肺功能，提高生活质量。     

Evaluation of excised lung gas volume measurements in animals with genetic or induced emphysema

Emphysema, a leading cause of respiratory disability and mortality in humans, is characterized by destruction of alveolar walls and enlargement of airspaces. Animal studies are critical in understanding the pathogenesis of emphysema. However, current measurements of airspace enlargement and emphysema in small laboratory animals are labor intensive and may not be sensitive enough for measuring alterations in lung function and structure at the early stages of emphysema. In this study, we have investigated the excised lung gas volume (ELGV) measurement as a potential index for determining airspace enlargement in pallid mice with developing emphysema, in tight-skin mice with developed emphysema, or in Wistar rats with emphysema induced by an intratracheal instillation of pancreatic elastase. Our results showed that values of both ELGV per lung and per gram lung tissue were significantly increased in all three emphysema models, compared to control. The ELGV values were correlated well with morphometric evaluation of emphysema. Variations in transpulmonary pressures caused by different termination procedures were critical factors influencing the ELGV values. The present study demonstrates that ELGV measurement is a simple and sensitive method to monitor the development of emphysema.     

Effect of increased diaphragm activation on diaphragm power spectrum center frequency

Increased transdiaphragmatic pressure, reduced muscle blood flow, and increased duty cycle have all been associated with a reduction in the center frequency (CFdi) of the diaphragm's electrical activity (EAdi). However, the specific influence of diaphragm activation on CFdi is unknown. We evaluated whether increased diaphragm activation would result in a greater decline in the CFdi when pressure-time product (PTPdi) was kept constant. Five healthy subjects performed periods of intermittent quasi-static diaphragmatic contractions with a fixed duty cycle. In separate runs, subjects targeted transdiaphragmatic pressures (Pdi) by performing end-inspiratory holds with the glottis open and expulsive maneuvers at end-expiratory lung volume (EELV). Diaphragm activation and pressures were measured with an electrode array and balloons mounted on an esophago-gastric catheter, respectively. The EAdi, which was 25+/-8%(S.D.) of maximum at EELV, increased to 61+/-8% (P<0.001) when an identical Pdi (averaging 31+/-13 cmH2O) was generated at a higher lung volume (77% of inspiratory capacity). The latter was associated with a 17% greater decline in CFdi (P=0.012). In order to reproduce at EELV, the decrease in CFdi observed at the increased lung volume, a two-fold increase in PTPdi was required. We conclude that CFdi responds specifically to increased diaphragm activation when pressure-time product remains constant.     

Assessing effects of PEEP and global expiratory lung volume on regional electrical impedance tomography

Objective: This study was performed to assess the value of electrical impedance tomography (EIT) as an indicator of tidal (V_T) and end expiratory lung volume (EELV).

Methods: EIT measurements were performed in seven healthy piglets during constant tidal volume ventilation at incremental and decremental positive end-expiratory pressure (PEEP) levels. Tidal impedance changes were calibrated to volume using V_T calculated from flow at the airway opening. Simultaneously, calibrated respiratory inductive plethysmography was used to measure EELV changes, and used as a reference standard.

Results: EIT systematically underestimated both V_T and EELV changes when EELV deviated from the level at which it was calibrated. Calculated over the entire pressure–volume curve, EIT systematically underestimated V_T by 28 ml, with a precision from ?16 to 72 ml. EELV was systemically underestimated by 406 ml, with a precision of ?38 to 849 ml. Nonlinear recruitment in the ventral regions of the lungs was the main cause of this underestimation.

Conclusions: Tidal and end-expiratory changes in pulmonary impedance reflect corresponding changes in lung volume, but the increasing underestimation with increasing lung volume should be taken into account in the analysis of EIT data.     

Experimental evaluation of the optimal tidal volume for simultaneous pacing of the diaphragm and respiratory muscles

Because of problems with pacing devices, surgical procedures, and diaphragm fatigue in pacing therapy of the phrenic nerve, we performed simultaneous pacing of the diaphragm alone and of multiple respiratory muscles in dogs and evaluated the optimal tidal volume. After intravenously anesthetizing 20 dogs with an average weight of 11kg, their tidal volume was measured with a spirometer to obtain control values. In the first 4 dogs, electrodes were sutured to the diaphragm and the optimal voltage, pulse width, and output to maximize tidal volume were determined. In the remaining 16 dogs, we stimulated individual canine respiratory muscles, i.e., the diaphragm, the rectus thoracis, and intercostal muscles 3-5 and simultaneously stimulated the diaphragm and the rectus thoracis; the diaphragm and intercostal muscles; the rectus thoracis and the intercostal muscles; or the diaphragm, rectus thoracis, and intercostal muscles. We compared a group in which a counterelectrode was positioned in each muscle group (group A) with a group in which no counterelectrode was used (group B). The best tidal volume was obtained at 10V, 50Hz, and a pulse width of 1.0ms. All the respiratory muscle pacings yielded better tidal volumes in group B than in group A. The greatest tidal volume was obtained with the rectus thoracis and intercostal muscle combination, suggesting the possibility of being able to reduce diaphragm fatigue by alternate pacing of these muscles and the diaphragm.     

急性高碳酸血症对膈肌功能的影响

本文用电刺激犬膈神经（ＰＮＳ）、记录经膈压（Ｐｄｉ）－刺激频率（Ｆ）曲线、分析自主呼吸膈肌肌电频谱（ＥＭＧｄｉ）的方法，研究急性ＣＯ２潴留对膈肌功能的影响，并探讨ｐＨ值在其中的作用。发现：１．急性ＣＯ２潴留使Ｐｄｉ进行性下降、Ｐｄｉ－Ｆ曲线右移，ＥＭＧｄｉ频谱改变；２．维持正常的ｐＨ值可减轻Ｐｄｉ、ＥＭＧｄｉ的改变。提示急性ＣＯ２潴留严重损害膈肌功能，ｐＨ的变化于其中起重要作用。     

A sigmoidal fit for pressure-volume curves of idiopathic pulmonary fibrosis patients on mechanical ventilation: clinical implications

OBJECTIVE:

Respiratory pressure-volume curves fitted to exponential equations have been used to assess disease severity and prognosis in spontaneously breathing patients with idiopathic pulmonary fibrosis. Sigmoidal equations have been used to fit pressure-volume curves for mechanically ventilated patients but not for idiopathic pulmonary fibrosis patients. We compared a sigmoidal model and an exponential model to fit pressure-volume curves from mechanically ventilated patients with idiopathic pulmonary fibrosis.

METHODS:

Six idiopathic pulmonary fibrosis patients and five controls underwent inflation pressure-volume curves using the constant-flow technique during general anesthesia prior to open lung biopsy or thymectomy. We identified the lower and upper inflection points and fit the curves with an exponential equation, V = A-B.e^-k.P, and a sigmoid equation, V = a+b/(1+e^-(P-c)/d).

RESULTS:

The mean lower inflection point for idiopathic pulmonary fibrosis patients was significantly higher (10.5±5.7 cm H₂O) than that of controls (3.6±2.4 cm H₂O). The sigmoidal equation fit the pressure-volume curves of the fibrotic and control patients well, but the exponential equation fit the data well only when points below 50% of the inspiratory capacity were excluded.

CONCLUSION:

The elevated lower inflection point and the sigmoidal shape of the pressure-volume curves suggest that respiratory system compliance is decreased close to end-expiratory lung volume in idiopathic pulmonary fibrosis patients under general anesthesia and mechanical ventilation. The sigmoidal fit was superior to the exponential fit for inflation pressure-volume curves of anesthetized patients with idiopathic pulmonary fibrosis and could be useful for guiding mechanical ventilation during general anesthesia in this condition.     

缺氧对家兔肺表面张力—表面积和压力—容量关系的影响

为分析缺氧状态下,潮气呼吸时呼吸力能关系的变化,结合以往实验,本文初步探讨了家免呼吸机械力能的变化与不同缺氧方式的关系。从实验中看到,急性缺氧明显提高呼吸做功,肺顺应性下降。从对呼吸压(P)—呼吸容量(V)滞后环的分析发现,急性缺氧家兔P—V滞后环的负载枝明显延长(5.2±0.6mm),与对照组(3.5±1.1mm)相比,增加了49%(P<0.01)。5天间断缺氧适应后,各项指标基本恢复到对照组水平。15天适应性缺氧效果不明显,可能与慢性缺氧反应有关。采用改良的Wilson方法(J Appl Physiol 1982;53:1512.),我们发现,作为潮气呼吸量的函数,表面张力的变化明显地受到不同缺氧条件的影响(组间比较P<0.01)。本实验提示,本文所选之分析潮气呼吸状态的机械力能关系变化的方法可靠;呼吸力能关系的变化与缺氧条件下,肺泡表面活性物质的变化有着密切的联系。     

Transpulmonary pressure and lung volume of the cat and the newborn: removal of cardiac effects with a digital filter

Dynamic lung compliance is a measure of the elastic properties of the lungs in the normal breathing range and is measured as the relationship between the transpulmonary pressure changes and the corresponding changes in lung volume. This relationship is given as a pressure-volume loop, from which the compliance is calculated as the slope of the line joining the end points of the loop. Owing to cardiac interference, which is superimposed on the normal pressure and volume signals, the compliance loops are often severely distorted, making it difficult to establish the end points in the loop. Therefore it is necessary to preprocess the measured data so that the superimposed cardiac pulsations are eliminated. In the investigations that are described in this paper, we have applied digital filtering techniques to recover compliance loops resulting solely from respiratory origin. The design method of a digital filter based on ‘windowing’ technique is discussed. The method is applied for filtering transpulmonary-pressure and lung-volume data obtained from experiments with cats and neonates. The effectiveness of digital filtering in recovering the compliance loops which are contaminated by the presence of cardiac pulsations is shown.     

Effect of plasma volume on thermoregulation in the dog

Panting thresholds, plasma volume (PV) changes and cardiac filling pressure were studied during thermal dehydration in control, water deprived (WD) and hypovolemic (PEG) dogs. WD and PEG dogs showed a delayed panting threshold, apparently due to hypovolevoia. Initiation of heat stress however resulted in a transient plasma expansion in all dogs. Cardiac filling pressure did not change.Permanent address: Dept. of Physiology, Haddassah School of Medicine and Dental Medicine, The Hebrew University, Jerusalem, Israel.     

Effect of acceleration on distribution of lung perfusion and on respiratory gas exchange

Summary Application of new technical and methodological development as respiratory mass spectrometry and double nuclide perfusion scintigraphy results in more detailed knowledge of the effect of accelerational forces on lung perfusion and respiratory gas exchange.For evaluation of some details of lung perfusion and respiratory gas exchange 20 healthy male subjects were exposed to prolonged hypergravitational stress (2 min,+G _z,+G _x or–G _y). Distribution of lung perfusion was measured by means of double nuclide perfusion scintigraphy using^99mTechnetium- and¹³¹Iodinemicrospheres allowing the registration of 2 phases of pulmonary perfusion in the same subject.PAO₂ andPACO₂ were measured by continuous mass spectrometrical registration andPaO₂,PaCO₂ and pHa were determined from arterial blood samples polarographically and electrometrically, respectively. Measurements were performed in the pre-run, in the run and partly in the post-run period, too.Depending on the magnitude and direction of the gravitational vector blood volume shifts within the lungs. Using computer evaluation of the scintiscans, it is possible to determine the magnitude of the normal-, hypo- and hyperperfused lung regions: for the extreme case of –4G _y only 3% of the 47% left lung perfusion at rest persists.During+G _z-acceleration thePaO₂ decreases linearily for approximately 10 Torr/+1G _z,PAO₂ increases by about 5 to 7 Torr/+1G _z andAaDO₂ increases correspondingly from 10.4 Torr at rest to 60.1 Torr at+3G _z. ForPaCO₂ no significant change could be observed during acceleration up to+3G _z, whereasPACO₂ decreased significantly from 36.5 to 25.0 Torr in the same time;aADCO₂ increased correspondingly. No significant pHa change was observed during all +G _z runs up to+3G _z.Prolonged expiration during+G _z-acceleration reveals an amplification of the amplitude of the cardiogenic oscillations in the alveolar plateau of expiratoryPO₂ andPCO₂-curves. Furthermore the alveolar plateau slopes down depending on the gravitational stress and indicating large disturbances of the ventilation/perfusion ratio.     

Effect of graded changes in extracellular muscle volume on cardiovascular drives during static exercise

Summary The effects of graded changes in peripheral extracellular volume on heart rate and blood pressure during isometric exercise were studied in 12 healthy male subjects. Each subject performed four calf ergometer tests with each calf. In all tests, static plantar flexion of one foot was performed in a supine body position with the knee joint flexed to 90°. After a pre-exercise period of 18 min, during which the calf volume was manipulated, the subjects had to counteract a spring force of 120 N for 8 min. In the pre-exercise period the peripheral extracellular volume of the calf muscle to be tested was manipulated in four ways. Test 1: 15 min of rest in the exercise position. During the last 3.5 min, the calf volume was increased by venous congestion [80 mmHg (10.67 kPa) applied to the distal part of the thigh by pneumatic cuff]. Test 2: the same protocol as in test 1 but with 7.5-min venous congestion. Test 3: 15 min of venous congestion. Test 4: the calf volume was decreased by a negative hydrostatic pressure for 15 min (calf raised about 40 cm above heart level). To clamp the changed calf volume, the thigh cuff was rapidely inflated to 300 mmHg (40.0 kPa) at the end of the volume manipulation and the subjects remained resting for a further 3 min. In test 4, the leg of the subject was passively brought into the exercise position. The occlusion was maintained until 2 min after exercise. The calf volume manipulation led to changes ranging from +105 ml (test 3) to –134 ml (test 4) as measured by water displacement plethysmography. The blood pressure response to exercise was inversely related to the calf volume changes while the heart rate response during exercise showed no clearcut relationship to the pretreatments.     

肺移植供肺获取100例：冷缺血时间>6 h及肺减容对预后的影响*

背景：肺移植过程中供肺获取的手术技巧、冷缺血时间的上限以及供肺与受者胸腔大小不匹配等问题的处理有待进一步研究。 目的：总结肺移植中供肺获取的手术技巧,探讨冷缺血时间和肺减容对受者移植后各种并发症以及生存率的影响。 方法：回顾分析100例供肺获取和101例受者的临床资料,根据供肺冷缺血时间所有受者分为冷缺血时间< 6 h组或> 6 h组;另根据移植中是否出现供肺与受者胸腔大小不匹配分为肺减容组和对照组,不匹配的均行不同方式肺减容。分析冷缺血时间>6 h和肺减容对肺移植患者预后的影响。 结果与结论：100例供肺获取和101例肺移植均成功,其中1供者的左右肺分别移植给2例受者,共完成101例肺移植。除供肺冷缺血时间>6 h组原发性移植物失功发生率要高于< 6 h组(P < 0.05)外,其他各指标差异均无显著性意义(P > 0.05);肺减容组与对照组各临床指标差异亦无显著性意义(P > 0.05)。提示严格的供者选择、恰当的供肺减容以及尽量缩短供肺冷缺血时间可以有效防止受者移植后各种并发症的发生,提高肺移植成功率,改善患者预后。 关键词：肺移植;脑死亡;供者选择;器官保存液;围手术期 doi:10.3969/j.issn.1673-8225.2012.05.018     

Effect of nasal CPAP treatment on plasma volume, aldosterone and 24-h blood pressure in obstructive sleep apnoea

Polycythaemia, peripheral oedema formation and hypertension have classically been described in association with obstructive sleep apnoea (OSA). However, there is very limited information about blood volume in OSA and how it changes during long-term treatment with nasal continuous positive airway pressure (nCPAP). Plasma (PV) and red-cell volumes (RCV), 24-h ambulatory blood pressure (BP), 24-h natriuresis and morning plasma aldosterone, renin activity and atrial natriuretic peptide in 11 men with a mean age of 47 y (range 37–55), apnoea index (AI) of 55 (22–106), body mass index of 36 (30–43) and seated BP of ≥140/90 mmHg without any medication were measured. BP-measurements were repeated after 3 weeks and all measurements after 3 mo of nCPAP treatment. Aldosterone and 24-h mean heart rates decreased during treatment. Twenty-four-h BP decreased after 3 weeks but that decrease did not persist after 3 mo of treatment. There was a relationship between changes in night-time mean BP and PV and aldosterone. The haematocrit declined in every patient. No significant changes were found in the mean PV or RCV. They were in all instances lower than has earlier been described for normal, non-obese subjects. These data also suggest that OSA causes divergent individual disturbances in blood volume homeostasis which can be corrected by nCPAP.     

环境温度对指端容积脉搏波检测精度的影响

目的探讨环境温度对指端容积脉搏波的影响。方法用凉水将32名受试者手指温度降至20℃,检测其容积脉搏波,并用温度计实时检测温度,记录波形,至手指温度恢复到实验前测量数值。结果当被测部位温度在26～31℃时,所获得的容积脉搏波参数K′、K1′、K2′及容积脉搏波幅值均无显著差异。结论当手指温度高于26℃时可进行指端容积脉搏波的检测,在26～31℃检测获得的容积脉搏波的基本参数无显著差异。     

Effect of isotonic volume expansion on glomerular filtration rate and renal hemodynamics in the developing rat kidney

Young rats (20–24 days) and adult rats (4–5 days) were studied during hydropenia and volume expansion with regard to glomerular filtration rate (GFR) and the determinants of GFR. During hydropenia, GFR and renal blood flow (RBF) were significantly lower in younger than in adult rats both in absolute terms and when related to bodyweight. Equivalent degrees of volume expansion (6% of b. wt.) resulted in a much more pronounced increase in GFR and RBF in younger than in older rats. This suggests that the high renal vascular resistance in hydropenic young rats is primarily due to vasoconstriction. The relationship between the filtration rate of superficial nephrons and the total GFR was the same in hydropenic and volume expanded rats in both age groups. The tubular stop flow pressure, the calculated hydrostatic glomerular capillary pressure and ultrafiltration pressure in the afferent part of the glomerular capillaries was slightly lower in hydropenic young rats than in hydropenic adult rats. The pressures did not rise after volume expansion. It is concluded that the marked increase in GFR in volume expanded young rats is mainly due to increased renal plasma flow.     

Effect of one hour of passive cigarette smoking on lung function and airway responsiveness in adults and children with asthma

Summary We exposed 18 adults with bronchial asthma, 16 healthy controls and 11 children with asthma for 1 h either to ambient air (AA) or to environmental tobacco smoke (ETS). Exposure was performed at rest in an exposure chamber. Before and after exposure symptom scores and lung function were determined. After exposure bronchoprovocation tests with methacholine (adults) or histamine (children) were performed to determine the concentrations causing a 100% increase in SRaw (PC₁₀₀SRaw), and a 20% fall in FEV₁ (PC_2OFEV₁). In adult asthmatics mean (SD) SRaw before and after Sham was 8.8 (3.6) and 8.4 (3.6) cmH₂O · s, and mean FEV₁ (SD) was 3.18 (0.97) and 3.14 (0.9) 1, respectively. Before and after passive smoking mean SRaw (SD) was 7.5 (3.0) and 7.2 (2.7) cmH₂O · s, and mean FEV₁ (SD) was 3.31 (1.0) and 3.21 (0.88) 1, respectively. Geometric mean (SD) PC₁₀₀SRaw and PC_2OFEV₁ after Sham were 0.38 (4.5) and 0.29 (4.1) mg/ml, after passive smoking 0.39 (5.1) and 0.36 (4.7) mg/ ml, respectively. In healthy controls there was no consistent effect on the respective parameters during exposure. In children mean (SD) SRaw before and after Sham was 8.7 (3.6) and 9.0 (3.2) cmH₂O · s, and mean FEV₁ (SD) was 1.97 (0.32) and 1.98 (0.40) 1, respectively. Before and after passive smoking mean SRaw (SD) was 10.4 (5.3) and 9.4 (3.3) cmH₂O · s, and mean FEV₁ (SD) was 1.95 (0.37) and 1.94 (0.35) 1, respectively. Geometric mean (SD) PC₁₀₀SRaw and PC₂₀FEV₁ after Sham were 1.39 (3.0) and 0.70 (2.7) mg/ml, and after passive smoking 1.65 (2.5) and 0.96 (2.3) mg/ml, respectively. There were no significant differences in lung function and airway responsiveness between exposure to ambient air or ETS. The main symptoms during passive smoking were eye and nasopharyngeal irritation. Our observations suggest that in children and adults with mild to moderate bronchial asthma, 1 h of passive cigarette smoking does not cause airway obstruction or con sistent changes in bronchial responsiveness.Abbreviations AA ambient air (Sham) - ETS environmental tobacco smoke - SRaw specific airway resistance - FEV₁a one-second forced expiratory volume - PC₂₀FEV₁a provocative concentrations of histamine/methacholine to decrease FEV₁ by 20% - PC₁₀₀SRaw provocative concentrations of histamine/methacholine to increase SRaw by 100% Supported by Forschungsrat Rauchen und Gesundheit, Hamburg, Federal Republic of Germany     

Effect of Hematocrit on pressure-flow relations for perfused isolated lobes of the canine lung

Summary The effect of hematocrit on pressure-flow relations for the pulmonary circulation was studied by means of an isolated lung preparation. Lobes taken from mongrel dogs were perfused with autologous blood of hematocrits ranging from 23 to 75. The apparatus was of a closed circuit type, consisting of the lobe being perfused by means of a roller pump so that a series of steady flows could be obtained. Transpulmonary pressure was imposed by positive inflation. Venous pressure, fixed by the distal liquid overflow, was maintained at+10 cm H₂O while alveolar pressure was +5 cm H₂O. Thus, for most of the parenchyma conditions were consistent with Zone III as described by Westet al. The arterio-venous pressure difference was varied between 3 and 50 cm H₂O.For comparison, pressure-flow relations were obtained concurrently with a capillary viscometer capable of attaining wall shear rates of less than 1 sec^–1.In 12 alterations of hematocrit (concentrations and dilutions) with 9 lobes it was found without exception that (1) increasing the hematocrit causes a shift of the pressure-flow curve in the direction of decreased flow and (2) decreasing the hematocrit caused a shift of the curve in the direction of increased flow. Analysis showed these changes to be statistically significant. Some evidence was also found that pressure-flow curves become more non-linear as hematocrit is increased.Supported in part by financial aid from the High Authority of the European Coal and Steel Community and the Délégation Générale à la Recherche Scientifique (Grant No. 66-00-442).