Breath-holding Method Research Articles

Reproducibility of organ position using voluntary breath hold method with spirometer during extracranial stereotactic radiotherapy

Reproducibility of organ position using voluntary breath hold method with spirometer during extracranial stereotactic radiotherapy

A new irradiation system for lung cancer: patient’s self-breath-hold and self-switching radiation-beam on and off without any respiratory monitoring devices

Purpose: It is helpful to irradiate a lung tumor under a breath-hold for a reduction of planning target volume(PTV). To develop a simple and efficient breath-hold radiation technique for lung cancer, we made three purposes. 1) To compare the reproducibility of tumor-position under a breath-hold by a patient’s self-estimation with that under a breath-hold by a radiation technologist’s instruction. 2) To develop a switch which enable a patient to turn the radiation-beam on and off. 3) To evaluate the reproducibility of a tumor-position in the radiation field with a patient’s self-breath-hold and self-switching radiation-beam. Materials and Methods: Twenty patients with lung cancer were enrolled in this study. All patients were taught sufficiently how to hold the breath at a same inspiration phase with showing a fluoroscopy of respiratory motion before evaluation. CT images were obtained with 2mm-thickness in the vicinity of the tumor under a series of the breath-hold by a radiation technologist’s instruction and another series of the breath-hold by a patient’s self-estimation. CT was repeated three times with each breath-hold method. Differences of tumor position on CT images were measured in three dimensions with a CT analyzing menu. We have newly developed a switch which was connected directly to the console box of linac ( EXL-15DP; Mitsubishi Electric, Tokyo, Japan). It enables a patient to turn radiation beam on and off freely and repeatedly during a term designated by a radiation technologist. Ten real-time portal images were taken for each patient during irradiation under a patient’s self-breath-hold and self-switching radiation-beam, and the accuracy of reproducibility of the tumor position in the radiation field was visually evaluated. Results: The average of maximum differences of the tumor position in three series of 20 patients under the breath-hold by a radiation technologist’s instruction was 3.0 mm in cranio-caudal direction, 2.1mm in antero-posterior direction and 2.3mm in right-left direction. And that in three series under the breath-hold by a patient’s self-estimation was 2.3mm in cranio-caudal direction, 1.4mm in antero-posterior direction and 1.4mm in right-left direction, respectively. A standard deviation of these differences was larger in the method of breath-hold by a radiation technologist’s instruction than in the method of breath-hold by a patient’s self-estimation. And these differences were larger in tumors of lower lung field than upper lung field. There was statistically significant difference between two methods of breath-hold. The actual switching of the radiation beam was delayed less than 0.1 second behind the patient’s switching. All portal images of 20 patients had a visually sufficient accuracy of tumor position in the radiation field with a difference less than 3mm between a planned position and actual tumor positions. Conclusion: The reproducibility of tumor position under patient’s self breath-hold without any respiratory monitoring devices had a satisfactory accuracy with a difference of tumor position less than 3mm in all directions. The method of breath-hold by a patient’s self-estimation was more accurate than that by a radiation technologist’s instruction. Our newly developed switch which enabled patients to turn the radiation-beam on and off was useful with a good reproducibility under a breath-hold at patients’ pace. And it has an excellent time-efficiency because the irradiation starts at the initiation of patients’ breath-hold and continues irradiation as long as patients keep the breath-hold. This new irradiation system is simple (no need for a respiratory monitoring device) and useful for irradiation of lung cancer with reduced PTV and a sufficient reproducibility.

Breathing-synchronized radiotherapy program at the University of California Davis Cancer Center.

In this paper we present a complete description of the breathing synchronized radiotherapy (BSRT) system, which has been jointly developed between the University of California Davis Cancer Center and Varian Associates. BSRT is a description of an emerging radiation oncology procedure, where simulation, CT scan, treatment planning, and radiation treatment are synchronized with voluntary breath-hold, forced breath-hold, or breathing gating. The BSRT system consists of a breathing monitoring system (BMOS) and a linear accelerator gating hardware and software package. Two methods, a video camera-based method and the use of wraparound inductive plethysmography (RespiTrace), generate the BMOS signals. The BMOS signals and the synchronized fluoroscopic images are simultaneously recorded in the simulation room and are later analyzed to define the ideal treatment point (ITP) where organ motion is stationary. The BMOS signals at ITP can be used to gate a CT scanner or a linear accelerator to maintain the same organ configuration as in the simulation. The BSRT system allows breath-hold or gating. This dual role allows the system to be applicable for a variety of patients, i.e., the breath-hold method for those patients who can maintain and reproduce the ITP, and the forced breath-hold or gating method for those who are not ideal for voluntary breath-hold.

Cerebrovascular Reactivity Evaluated by Transcranial Doppler: Reproducibility of Different Methods

Transcranial Doppler is routinely used to assess the cerebrovascular reactivity, despite scarce information on its reproducibility. We evaluated the reproducibility of cerebrovascular reactivity measurements by this method utilizing different vasodilatory and vasoconstrictor stimuli. The cerebrovascular reactivity was measured in 45 healthy volunteers during hypercapnia induced by inhalation of a mixture of 5% CO₂ and 95% O₂, breath holding and rebreathing, and during hypocapnia induced by voluntary hyperventilation. Three sets of measurements were performed at times 0, 1, and 24 h to assess the within-observer short- and long-term reproducibility. The reproducibility was analyzed using the intraclass correlation coefficient. For the CO₂ inhalation method, a good short-term (r_I = 0.55; 95% CI = 0.39–0.68) and a good long-term (r_I = 0.43; 95% CI = 0.25–0.59) reproducibility was found. For the breath-holding method a good short-term agreement was found (r_I = 0.41; 95% CI = 0.22–0.57), while the long-term reproducibility was poor (r_I = 0.17; 95% CI = –0.03–0.36). Rebreathing showed a fair (r_I = 0.31; 95% CI = 0.11–0.48) short-term and a poor (r_I = 0.17; 95% CI = –0.03–0.36) long-term reproducibility. For voluntary hyperventilation, the short-term reproducibility was good (r_I = 0.53; 95% CI = 0.36–0.66), and the long- term reproducibility was fair (r_I = 0.31; 95% CI = 0.11–0.48). In our study, CO₂ inhalation and voluntary hyperventilation had the highest reproducibility and should be preferred when assessing cerebral vasoreactivity, especially in follow-up studies.

A change in the pulmonary diffusing capacity (DL/Va) at rest and during exercise for two different postures

1073 The purpose of the present study was to compare the pulmonary diffusing capacity (DL/Va) at rest and during exercise for upright and supine postures. Six healthy male subjects (age: 23.7 ± 1.1 yr; height: 174.5±2.0 cm; body weight: 73.0 ± 5.4 kg) were studied. All subjects were nonsmokers who did not usually exercise. DL/Va was measured at rest and during intermittent incremental maximum exercise on a bicycle ergometer in both postures using the Breath-holding method (Forster et al., 1954). The resting values of DL/Va (6.29 ± 0.70 ml/min/mmHg/l) in the supine posture were higher than the values (5.60 ± 0.52 ml/min/mmHg/l) in the upright posture (p<0.05). Maximum oxygen uptake, maximum ventilation, maximum work load, and exercise time in the upright posture were higher than in the supine posture (p<0.05). DL/Va during submaximum exercise increased with heart rate, oxygen uptake, ventilation, oxygen pulse, and DL/Va in the supine posture were higher than in the upright posture for the same work (p<0.05). However, there was no significant difference in the maximum DL/Va for the upright (8.93±0.61 ml/min/mmHg/l) and supine postures (8.82±0.29 ml/min/mmHg/l). From these results, it was suggested that influences on the blood flow are greatly reflected in the DL/Va at rest and during exercise, and the diffusion in the supine posture is more effective than in the upright posture.

Full Range of Vasodilation Tested by Transcranial Doppler in the Differential Diagnosis of Vascular and Alzheimer Types of Dementia

The aim of this study is to validate whether measuring the cerebral vasomotor response with the breath-holding method can be a useful technique in the differentiation of vascular and Alzheimer types of dementia. We adopted the clinical and neuropsychological diagnosis of dementia according to DSM-IV criteria as the standard diagnosis against which our method was compared. Resting middle cerebral artery velocity, its rate of increase on breath holding and its decrease on hyperventilation (full range of vasodilation, FRV) were measured using a transcranial Doppler (TCD) velocimeter on both sides in a prospective study on 32 age-matched controls, 36 patients diagnosed with Alzheimer type dementia, and 31 vascular dementia (VD) patients. A total of 186 vessels were studied in 99 patients. A high level of significance (p < 0.001) was noted in the FRV in the differentiation between the VD group and the other two groups, on both sides and in both sexes. By taking a statistically optimal cutoff point of 70%, the sensitivity and specificity of the FRV test for the diagnosis of VD are 84.5 and 93.0% respectively. Measurements of hemodynamic reserve using the cerebral perfusion reserve test assessed by TCD could provide a way to detect demented individuals with underlying vascular mechanism of dementia, but would not offer prognostic data or differentiate between varying degrees of dementia.

Transcranial Doppler assessment of cerebrovascular reactivity in symptomatic and asymptomatic severe carotid stenosis.

Some studies have suggested a link between impaired cerebral hemodynamics and stroke in patients with carotid stenosis. The aim of this study was to assess the effects of severe carotid stenosis on cerebrovascular reactivity and the possible changes after endarterectomy. Using bilateral transcranial Doppler ultrasound, we studied the changes of flow velocity after hypercapnia in the middle cerebral arteries of 10 control subjects and 24 patients (13 symptomatic and 11 asymptomatic) with unilateral severe carotid stenosis before and after endarterectomy. Cerebrovascular reactivity was evaluated with the breath-holding index (BHI). Before endarterectomy, BHI (mean value +/- SD) was significantly lower (P < .001) in the stenotic side of symptomatic patients (0.40 +/- 0.2) than in control subjects (1.12 +/- 0.3), the stenotic side of asymptomatic patients (0.80 +/- 0.4), and the normal side of both symptomatic (0.93 +/- 0.3) and asymptomatic ultrasonics (1.03 +/- 0.2) patients. On the other hand, no significant difference in BHI was detected in control subjects, on the normal side of symptomatic and asymptomatic patients, and the stenotic side of asymptomatic patients. After endarterectomy, BHI significantly increased (P < .0001) on the stenotic side of symptomatic patients (1.06 +/- 0.2) while remaining substantially stable on the normal side of both symptomatic and asymptomatic patients and on the stenotic side of asymptomatic patients. These findings suggest that the study of cerebrovascular reactivity to hypercapnia may be relevant in evaluating the functional effects of carotid stenosis. Further investigations are needed to confirm the reliability of the breath-holding method in the selection of patients who might benefit most from carotid endarterectomy.

Role of Endogenous Nitric Oxide in Airflow Obstruction in Smokers

The aim of this study was to examine the relationship between endogenous nitric oxide (NO) level and airflow obstruction in smokers using single-breath measurement of exhaled NO with the sequential breath-holding method. A university hospital. Nine nonsmoking and ten smoking healthy volunteers. NO in exhaled air was measured using a chemiluminescence analyzer. Pulmonary function tests were performed using an autospirometer. The level of exhaled NO was higher in nonsmokers than in smokers, and the difference became larger as the breath-holding time increased. To evaluate the correlation between endogenous NO level and the degree of airflow obstruction in smokers, we used a new parameter, the NO concentration difference (delta NO). Our findings indicate that reduced level of NO in exhaled air is an indicator of decreased NO synthesis within the respiratory system and is associated with the development of airflow obstruction in smokers (r = 0.678; p < 0.01). delta NO is a good indicator of the synthesis of endogenous NO within the respiratory system, and it appears likely that the reduced synthesis of NO may be a contributing factor to airflow obstruction in smokers.

Vasomotor reactivity and pattern of collateral blood flow in severe occlusive carotid artery disease.

The compromise of cerebrovascular autoregulation in severe occlusive carotid artery disease depends on the functional capacity of collateral pathways. In previous reports correlating hemodynamic disturbances with collateral pathways, collateral blood supply was often evaluated by invasive cerebral angiography. In this study noninvasive transcranial Doppler ultrasound was used to determine both collateral pathways and vasomotor reactivity. With the use of blood flow direction, compression tests, and evident side-to-side asymmetries of blood velocities, the collateral supply through the anterior and posterior communicating arteries, the ophthalmic artery, and leptomeningeal anastomoses was evaluated by transcranial Doppler ultrasound in 48 patients (42 men, 6 women; mean +/- SD age, 59 +/- 9 years) with occlusion (n = 36) or stenosis of more than 90% (n = 12) of one internal carotid artery. Ipsilateral vasomotor reactivity was determined by the percent increase of middle cerebral artery mean blood velocity with the use of (1) the breath-holding maneuver and (2) acetazolamide (1 g IV) as vasodilatory stimulus. Additional stenoses (50% to < 90%) of the contralateral internal carotid artery were present in 20 of the 48 patients. Vasomotor reactivity was not affected by the presence of a contralateral internal carotid artery stenosis. Both vasodilatory stimuli similarly indicated poor vasomotor reactivity when an ophthalmic or a leptomeningeal pathway accompanied an anterior communicating artery pathway compared with a lone anterior communicating artery pathway (P < .05). The acetazolamide challenge indicated significantly better preserved vasomotor reactivity when blood supply was provided through a lone anterior communicating artery pathway (66 +/- 30%) than through an anterior and posterior communicating artery pathway (33 +/- 20%, P < .05), whereas the breathholding method failed to show such a difference. The presence of an ophthalmic artery pathway may provide the first evidence of disturbed vasomotor reactivity. The use of cerebral angiography to evaluate collateral pathways must be considered carefully since transcranial Doppler ultrasound is a reliable noninvasive alternative.

Utility of complete dead space washout by real-time gas analysis in the measurement of transfer factor in patients with chronic airflow limitation.

Chronic obstructive pulmonary disease (COPD) is associated with impaired gas mixing and increased dead space, but little is known about the effect of improving alveolar gas sample by complete correction of dead space in an attempt to significantly improve the final result of transfer factor compared with standard guidelines of the European Respiratory Society (ERS) and American Thoracic Society (ATS). By using a rapid infrared analyzer, TLCO was measured by the single breath method in 152 COPD patients at different stages of severity (FEV1:57% predicted; CI 95%:24-91). Standard washout volume of 0.75 liter was insufficient to clear phases I and II in 36 patients (23.7%). In 19 subjects (12.5%), a washout volume larger than 1 liter was necessary for complete dead space clearance, although in these patients, correction visually adequate to complete clear phases I and II resulted in higher TLCO values. Only in 5 patients (3.3%) did the final result change by more than 5% from the previous value. A vital capacity higher than 3 liters, rather than the degree of airflow limitation was a better predictor for larger washout volume requirements. We conclude that in the measurement of TLCO by the breathholding method, ERS and ATS recommendations for washout volume can be safely used for clinical purposes in a wide range of patients with mild to severe obstruction.

Respiratory and postprandial changes in portal flow rate: assessment by phase contrast MR imaging.

The objective of this study was to investigate the variability of several different phase contrast (PC) magnetic resonance techniques and duplex Doppler imaging (DDI) for measuring portal flow rate (PFR) with different patterns of respiration before and after a standard meal. PFR was measured in nine normal volunteers in both fasting and postprandial states, using both 2D and cine PC MR techniques. Two-dimensional PC technique was performed with and without breath-hold (BH). Four different patterns of BH (relaxed maximal inspiration, expiration, Valsalva maneuver, and Müller or reversed Valsalva) were used. Cine PC technique was performed without BH. DDI measurement of PFR was done in the fasting state with relaxed inspiration. PFR measurements made by means of PC MR techniques varied, depending on BH method, and were systematically less than those obtained by DDI. PFR measured during inspiration was significantly less than that measured during expiration and other respiratory maneuvers (P < .03). PFR increased significantly after a meal for PC and Doppler measurements, with a range of mean increases of 24 to 74%. Two-dimensional PC MR imaging techniques yielded differing measurements of PFR, depending on whether they were done with or without BH, as well as on the pattern of BH. PC mean measures of PFR were consistently less than those of DDI. The physiologic inspiratory decreases and postprandial increases of the PFR were evident from 2D and cine PC MRI techniques, as well as with DDI.

Epidural Anesthesia Affects Pulse Oximeter Readings and Response Time

We investigated the effects of epidural anesthesia on pulse oximeter readings (Spo2) and response time because this type of anesthesia causes significant changes in microcirculation at measurement sites. Twenty patients were divided into lumbar epidural (L-EPI;n=10) and the cervical epidural (C-EPI;n=10) groups. Spo2 and skin blood flow (SBF) were measured at the finger and toe simultaneously by pulse oximeter and laser Doppler flowmeter, respectively. Data were collected before and after epidural anesthesia for 1 min and the response time was calculated by the difference between the finger and toe using the breath-holding method. Epidural anesthesia increased SBF in the blocked area and decreased it in the nonblocked area in both groups (P<0.01, respectively). In the L-EPI group, Spo2 was increased at the finger (P<0.05) and decreased at the toe (P<0.05). In the C-EPI group, Spo2 at both the finger and toe was decreased by the anesthesia. ΔSpo2 (Spo2 at the finger minus Spo2 at the toe) was increased in the L-EPI group (P<0.05) and decreased in the C-EPI group (P<0.01). The difference in the response time became larger in the C-EPI group and smaller or opposite in the L-EPI group after anesthesia. The difference in response time and SBF were significantly correlated (r=0.71;P<0.05). These results indicated that epidural anesthesia lowerd Spo2 and shortened the response time through vasodilation in the blocked area and caused the opposite reactions in the nonblocked area through compensatory vasoconstriction.

230.腹部領域における呼吸下DSA撮影の検討

230.腹部領域における呼吸下DSA撮影の検討

Epidural anesthesia affects pulse oximeter readings and response time.

We investigated the effects of epidural anesthesia on pulse oximeter readings (Spo2) and response time because this type of anesthesia causes significant changes in microcirculation at measurement sites. Twenty patients were divided into lumbar epidural (L-EPI;n=10) and the cervical epidural (C-EPI;n=10) groups. Spo2 and skin blood flow (SBF) were measured at the finger and toe simultaneously by pulse oximeter and laser Doppler flowmeter, respectively. Data were collected before and after epidural anesthesia for 1 min and the response time was calculated by the difference between the finger and toe using the breath-holding method. Epidural anesthesia increased SBF in the blocked area and decreased it in the nonblocked area in both groups (P<0.01, respectively). In the L-EPI group, Spo2 was increased at the finger (P<0.05) and decreased at the toe (P<0.05). In the C-EPI group, Spo2 at both the finger and toe was decreased by the anesthesia. ΔSpo2 (Spo2 at the finger minus Spo2 at the toe) was increased in the L-EPI group (P<0.05) and decreased in the C-EPI group (P<0.01). The difference in the response time became larger in the C-EPI group and smaller or opposite in the L-EPI group after anesthesia. The difference in response time and SBF were significantly correlated (r=0.71;P<0.05). These results indicated that epidural anesthesia lowerd Spo2 and shortened the response time through vasodilation in the blocked area and caused the opposite reactions in the nonblocked area through compensatory vasoconstriction.

Pulmonary diffusing capacity after maximal exercise.

To determine the effect of maximal exercise on alveolocapillary membrane diffusing capacity (Dm), 12 professional handball players aged 23.4 +/- 3.3 (SD) yr were studied before and during early recovery from a progressive maximal exercise [immediately (t0), 15 min, and 30 min (t30) after exercise]. Lung capillary blood volume and Dm were determined in a one-step maneuver by simultaneous measurement of CO and NO lung transfer (DLCO and DLNO, respectively) with use of the single-breath breath-hold method. At t0, DLCO was elevated (13.1 +/- 12.0%; P < 0.01) but both DLNO and Dm for CO remained unchanged. Between t0 and t30, both DLCO and DLNO decreased significantly. At t30, DLCO was not different from the control resting value. DLNO (and consequently Dm for CO) was significantly lower than the control value at t30 (-8.9 +/- 8.1%; P < 0.01). Lung capillary blood volume was elevated at t0 (18.0 +/- 19.0%; P < 0.01) but progressively decreased to near control resting values at t30. Differences in the postexercise kinetics of both DLCO and DLNO point to a role of the transient increase in pulmonary vascular recruitment during the recovery period. We concluded that Dm was somewhat decreased in the 30 min after maximal exercise of short duration, but the exact pulmonary mechanisms involved remain to be elucidated.

Pulmonary diffusion limitation after prolonged strenuous exercise

To determine the effect of strenuous prolonged exercise on alveolo-capillary membrane diffusing capacity, 11 marathon runners aged 37 ± 7 years (mean ± SD) were studied before and during early recovery (28 ± 14 min) from a marathon race. Lung capillary blood volume (Vc) and the alveolo-capillary diffusing capacity (Dm) were determined in a one-step maneuver by simultaneous measurements of CO and NO lung transfer (D l CO and D l NO, respectively) using the single breath-holding method. After the race, both D l CO and D l NO were significantly decreased in all subjects − 10.9 ± 4.8%, P < 10 −4 and −29.0 ± 11.1%, P < 10 −4, respectively). The mean value of the derived Dm CO decreased by −29.3 ± 11.1 %, whereas Vc had no entirely returned to control resting value. Although these results do not indicate the detailed mechanism involved, interstitial lung fluid was suspected to accumulate, particularly in alveoli, during the race. We concluded that the high overall work load and the extended duration of the exercise both contributed to a transient change in the structure of the alveolo-capillary membrane thereby affecting the diffusing capacity of the alveolo-capillary membrane.

Carbon Monoxide Diffusing Capacity of the Lungs Determined by Single-Breath and Steady-State Exercise Methods

We measured carbon monoxide diffusing capacity of the lungs (DL,CO) by both the resting single-breath (SB) and steady-state (SS) exercise methods in 95 patients referred for pulmonary function testing. A 10-second breath-holding method was used for the SB test. DL,CO (SS) was measured during the last minute of a 3-minute exercise test on a 9-inch step. Results of the two methods showed good agreement, the SB-SS difference averaging -0.70 (SD, 3.39) ml/min per mm Hg. The difference between the two methods was not correlated with other measurements of pulmonary function except minute ventilation during the exercise performed in the DL,CO (SS) procedure. In a separate study of laboratory personnel, the day-to-day variabilities of the two tests were similar (SD, 1.4 ml/min per mm Hg). Alveolar volume obtained by helium dilution during the SB test was comparable to total lung capacity (TLC) estimated by multiple-breath nitrogen washout in patients without severe airway obstruction. In severe airway obstruction, the mean SB alveolar volume was 13.8% less than the TLC by nitrogen washout, a difference that may be useful as an indicator of inefficiency of gas mixing in the lungs. We conclude that the SB and SS exercise methods provide similar estimates of DL,CO in patients referred to a pulmonary function laboratory.

Changes in Pulmonary Diffusing Capacity at Rest under Various Conditions of Posture and Temperature in Male and Female

Changes in pulmonary diffusing capacity for carbon monoxide (DL), the diffusing capacity of the pulmonary capillary membrane (DM) and pulmonary capillary blood volume (VC) at rest were examined in eight adult subjects of both sexes by the breath-holding method under different posture and temperature conditions; i. e., in a supine position and a head-up position (45°) by the use of a tilting bed at three ambient temperatures of 15, 25 and 35°C. Under all these conditions, DL was closely related to changes in VC. Posture significantly affected DL and VC in both males and females, the degree of difference due to each posture in males being similar to that in females. Although the influence of temperature on DL and VC was significant in males, it was somewhat vague in females. The following causes of this phenomenon were suggested: the range of variation in the pulmonary arterial pressure due to thermal stimulation is narrow and the size of the lung is smaller in females than in males. The relation of DL to wide-spread changes in VC in both sexes showed the form of a curve, probably because the increase in VC mainly reflects the process of transformation of the pulmonary capillary from recruitment to dilation.

Lung tissue volume and blood flow by rebreathing theory

Rebreathing determinations of pulmonary tissue volume (Vt) and pulmonary capillary blood flow (Qc) are supplanting breath-holding methods because of the shorter time for data collection and better reproducibility. However, rebreathing methods have errors due to dead space (Vd), volume breathed (Ve), rebreathing rate (RR), as well as from uneven distribution between Vt, Qc, Ve, and alveolar volume (Va). These errors were studied by calculating Vt and Qc from a normal lung model with dimensions: Vt = 600 ml, Qc = 6 l/min, Ve = 2,000 ml, residual volume = 2,000 ml. Vd = 200 ml, and RR = 30/min. RR as slow as 10/min and Vd of 200 ml caused less than a 4% error in Vt and Qc. Increases in Vd to 1,000 ml overestimated Vt by 31% and underestimated Qc by 19%, but a simple correction for the decreased effective Va with the first breath reduced these errors to 8% and 13%, respectively. More rapid RR and larger Ve always decreased errors due to Vd. The uneven distribution reported in normal man due to gravitational forces caused a 4% error in Vt and a 1% error in Qc. Lung models constructed from reported data for uneven distribution inmore » severe obstructive lung diseases showed large errors in Vt (-13% to +46%) and smaller errors in Qc (-1% to -18%). Models of severe restrictive diseases generally gave marked underestimates of Vt (-3% to -64%). These data indicate that estimates of Vt and Qc have acceptable accuracy in normal man and subjects with moderate degree of uneven distribution, but large errors develop with more severe forms of lung disease.« less

A continuous method for measuring acetylene in expired gas using glow discharge and its application to assessment of pulmonary blood flow.

In order to measure a rapid change in pulmonary blood flow the suitability of a glow discharge gas analyser for the continuous analysis of C2H2 was examined. The analyser was originally designed for continuous analyses of O2 and CO2 in expired air. However, we found that it responded specifically to C2H2, when a gas mixture containing 5% O2, 40% CO2 with a balance of N2 was used as a carrier gas and a negative voltage of 20 V was applied to the proximal collector electrode against the distal. Under these conditions the C2H2 current was reproducible within 0.1 mmHg, the base line drift was smaller than 1 mmHg/hr and the 90% response time was about 0.6 sec. This method was applied to analysis of C2H2 in expired air in combination with a constant rate expiration technique. When a C2H2 gas mixture was inhaled and expired at a constant rate, the observed C2H2 curves agreed with the theoretical ones calculated at the pulmonary blood flow rates obtained separately with the conventional breath-holding method. The decay rate of the C2H2 curve showed a rapid change within 1.5 sec when exercise and a Valsalva-like maneuver were made during continuous expiration, suggesting a quick alternation in pulmonary blood flow.