Validation of the phase angle technique as an objective measure of upper airway obstruction

Thoraco-abdominal asynchrony (TAA) during upper airway obstruction (UAO) in small children can be documented by phase angle analysis of the Lissajous figure from the output of a noncalibrated respiratory inductance plethysmograph. Phase angle measurements have not been related to levels of inspiratory resistance, nor to the effect of breathing a 79% helium-21% oxygen mixture (heliox) during inspiratory resistance. We examined the effects of graded inspiratory loading (5-1000 cm H2O/L/sec) on TAA as measured by phase angle in 10 male, anesthetized, and intubated Rhesus monkeys, breathing room air and heliox. Phase angles increased with inspiratory loading from a baseline value of 22 +/- 3 degrees to 165 +/- 8 degrees at 1,000 cm H2O/L/sec resistance and correlated significantly with the level of inspiratory loading (r = 0.82). End-tidal carbon dioxide PETCO2 increased from 39 +/- 1 to 49 +/- 3 mm Hg at the highest load, but correlated only weakly with phase angle measurements (r = 0.60) and the level of inspiratory loading (r = 0.56). By changing to heliox breathing at the highest tolerated resistance, PETCO2 dropped significantly from 49 +/- 3 to 40.5 +/- 4 mmHg (P < 0.001) with no significant change in phase angles: 169 +/- 13 degrees and 165 +/- 8 degrees, respectively (P > 0.05). We conclude that heliox therapy for acute alveolar hypoventilation during UAO improves ventilation, but does not decrease TAA at high inspiratory resistance. Continuous monitoring of the relative changes in phase angles is useful to observe the severity of UAO in the early stages.(ABSTRACT TRUNCATED AT 250 WORDS)

Splanchnic venous pressure-volume relation during experimental acute ischemic heart failure. Differential effects of hydralazine, enalaprilat, and nitroglycerin

BACKGROUND

Vasodilator drugs have variable effects on veins and arteries. However, direct measurements of their effects on the splanchnic veins, perhaps the most important volume reservoir, have not been reported. We assessed the effect of acute heart failure and the subsequent administration of hydralazine, enalaprilat, and nitroglycerin on the splanchnic venous pressure-volume relation in intact dogs.

METHODS AND RESULTS

Experimental acute ischemic heart failure was induced in 19 splenectomized dogs by microsphere embolization of the left main coronary artery. Embolization was repeated until left ventricular end-diastolic pressure (LVEDP) reached 20 mm Hg and cardiac output decreased by 50%. The splanchnic vascular pressure-volume relation was determined by radionuclide plethysmography during the control stage, after acute heart failure had been established, and after administration of a vasodilator (hydralazine, enalaprilat, or nitroglycerin) at a dose sufficient to reduce mean aortic pressure by approximately 20%. Induction of acute heart failure was associated with a decrease in the splanchnic vascular volume from 100% to 86 +/- 2% and an increase in LVEDP from 6 +/- 1 to 21 +/- 1 mm Hg (P < .001). There was a parallel leftward shift of the splanchnic vascular pressure-volume curve. After the administration of hydralazine, enalaprilat, and nitroglycerin, the splanchnic vascular volumes increased from 86% to 88 +/- 3%, 96 +/- 3%, and 113 +/- 3%, respectively (P = NS, P < .01, and P < .001, respectively, versus heart failure). After drug administration, the LVEDPs were 18 +/- 2, 16 +/- 1, and 13 +/- 1 mm Hg (P = NS, P < .05, and P < .001, respectively, versus heart failure).

CONCLUSIONS

Acute heart failure was associated with a parallel leftward shift of the splanchnic venous pressure-volume relation (venoconstriction). Splanchnic (systemic) venoconstriction may in part explain the increased LVEDP during acute heart failure by displacement of blood to the central compartment. Subsequently administered enalaprilat and, to a greater degree, nitroglycerin produced splanchnic venodilation, thereby lowering LVEDP. Hydralazine had no significant effect on the splanchnic veins and only a modest effect on LVEDP. In this model, splanchnic capacitance changes appear to modulate change in left ventricular preload.

Finger systolic blood pressures: effects of cold provocation on the reference finger

Finger systolic blood pressure measured after cold provocation and ischemia of a digit is used to assist in the diagnosis of vibration-induced white finger, VWF. A reduction in finger systolic blood pressure after cooling is assumed to indicate vascular dysfunction. The percentage pressure change observed in the tested finger is often corrected for whole body effects (systemic systolic pressure changes) according to the pressure change measured in a reference finger. The commonly used method of correction is based on assumptions as to the causes of any changes occurring in the reference finger. It is assumed that the reference finger is not differentially susceptible to the cold provocation of the test finger, arising from either close proximity to the cold provocation or from a vascular disorder in the reference finger. An experiment has been undertaken to investigate the repeatability, over three days, of measurements of the arm systolic pressures of both arms and the finger systolic pressures in air of four fingers of both hands. The systolic pressures of both arms and of four fingers of one hand were also measured whilst the fifth finger of the same hand was subjected to cold provocation at 10 degrees C. Twelve healthy male subjects were rested in a supine position for 15 minutes in a room at 21-24 degrees C before measurements were taken. Finger systolic blood pressures were recorded using strain gauge plethysmography. The results show that the systolic blood pressure measurements were generally repeatable, but differed with measurement location. Cold provocation of the test finger had little consistent effect on the systolic pressures measured at other locations. The results are interpreted with regard to the correction of finger systolic pressure using a reference measurement.

Use of the air plethysmograph in the evaluation and treatment of patients with venous stasis disease

BACKGROUND

Some patients with venous stasis disease require physiologic testing of venous function for complete evaluation prior to and/or after treatment.

OBJECTIVE

To review basic uses of the air plethysmograph in evaluating patients with venous stasis disease.

METHODS

The air plethysmograph can be used to quantitate obstruction, reflux, and the effectiveness of the calf muscle pump.

RESULTS

Significant outflow obstruction is indicated by an outflow fraction of less than 35%. A venous filling index of 2 ml/second or greater indicates significant reflux. An ejection fraction of less than 40% is associated with poor calf muscle pump function.

CONCLUSIONS

The air plethysmograph can be used in the evaluation of patients with venous stasis disease to quantify venous abnormalities of obstruction, reflux, and poor muscle calf pump function.

Pressure sensor plethysmography: a method for assessment of respiratory motion in children

Noncalibrated respiratory inductance plethysmography has been used to measure respiratory function by calculation of the phase angle and, more recently, by determination of the ratio of each time to reach peak tidal expiratory flow to total expiratory time (TPEF/TE). Since TPEF/TE is known to be decreased in airway obstruction when derived from flow signals obtained by a pneumotachograph, we wanted to develop an alternative method to measure rib cage and abdominal respiratory movements. For this purpose, we used two pressure sensors attached to the skin above the umbilicus and in the right medioclavicular line at the fourth intercostal space: "pressure sensor plethysmography". We tested the ability of this method to assess thoracoabdominal asynchrony and TPEF/TE by comparison with respiratory inductance plethysmographic and pneumotachographic measurements in 30 children, aged 1-12 yrs, with airway obstruction. The mean difference (95% confidence interval (95% CI)) between phase angles obtained by respiratory inductance plethysmography and pressure sensor plethysmography was only -5.8 degrees (range -18.0 to +6.4 degrees). Similarly, all methods used to measure TPEF/TE agreed well: mean differences (95% CI) between pneumotachographic and respiratory inductance plethysmographic, pneumotachographic and pressure sensor plethysmographic, and respiratory inductance plethysmographic and pressure sensor plethysmographic measurements of TPEF/TE were +0.01 (range -0.05 to +0.06), -0.03 (-0.09 to +0.03) and -0.03 (-0.10 to +0.04), respectively. We conclude that pressure sensor plethysmography is a simple and noninvasive method, and suitable to measure thoracoabdominal asynchrony and TPEF/TE ratios as well as respiratory inductance plethysmography and pneumotachography.

[Plethysmechanomyography (PMG). A simple method for monitoring muscle relaxation]

Ideal evaluation of neuromuscular blockade can be done by mechanical or electromyographical registration of muscle contractions evoked by ulnar nerve stimulation. Unfortunately, devices needed for such registration are expensive or complicated to set up, and thus are not often used for routine monitoring in anaesthesia. In this study, we describe a simple and low-priced method permitting intra- and postoperative monitoring of neuromuscular blocking agents. The accuracy of plethysmomechanomyography (PMG) was evaluated by comparing simultaneous electromyographic (EMG) and plethysmographic measurements. METHODS. For plethysmographic registration of muscle response to nerve stimulation a simple infusion system is twisted there to five times around one hand and connected to an anaesthetic monitor via a pressure transducer. The drip chamber is fixed about 20 cm above the hand (Fig. 1). Then, the infusion system is then filled up-with physiologic saline solution and the clamp is nearly closed. Electric stimulation can be carried out using any nerve stimulator. Using this method, PMG mainly records the contractions of abductor digiti minimi muscle, but also partly those of the interossei. Evoked muscle contractions cause stretching of the infusion system, which leads to pressure changes proportional to the strength of contraction. The muscle response to "train-of-four" (TOF) stimulation of the ulnar nerve was recorded simultaneously by EMG and PMG in 11 patients (ASA class I or II) undergoing neurosurgical procedures and therefore requiring muscle relaxation. After induction of anaesthesia by injection of etomidate and fentanyl, supramaximal stimulation and control values (T0) were defined. Anaesthesia was maintained by supplementation with nitrous oxide/oxygen (1:2) and muscle relaxation was carried out with vecuronium. We used the integrated nerve stimulator of a Datex Relaxograph NMT-100 EMG monitor and proceeded to stimulate the ulnar nerve at the forearm with supramaximal strength. The PMG was registered by a Siemens Siredoc 220 printer connected to a Siemens Sirecust 1281 anaesthetic monitor. First twitch ratio (T1/T0) and TOF ratio (T4/T1) were calculated from these recordings. The EMG recordings were made by a Datex Relaxograph NMT-100 monitor, which automatically computes T1/T0 and T4/T1. The comparison of EMG and PMG values was carried out by simple linear regression. Statistical evaluation was performed using analysis of variance. RESULTS. A plethysmographically registered graph of the TOF-evoked muscle response is illustrated in Fig. 2. Simultaneous EMG and PMG recordings of onset and recovery from a nondepolarizing blockade are shown in Fig. 3. A strong positive correlation (P < 0.001) of EMG and PMG was found with correlation coefficients of 0.98 for T1/T0 and of 0.97 for T4/T1. The mean difference between values of both methods was 5%, maximally 18% (T1/T0) and 20% (T4/T1). CONCLUSIONS. Mechanomyography and EMG are well established methods of neuromuscular monitoring. Our data demonstrate that PMG provides a reliable measurement of neuromuscular transmission that correlates well with EMG. Since only materials of daily use in anaesthesia are needed, no substantial costs will arise when the plethysmographic method of measurement is used for routine anesthetic monitoring.

Lack of contribution of nitric oxide to basal vasomotor tone in heart failure

Patients with heart failure have reduced forearm vasodilator responses when endothelial cell nitric oxide production is stimulated by muscarinic agonists. The aim of this study was to determine if activity of the nitric oxide pathway was also abnormal under basal conditions. Forearm blood flow (FBF) was measured with strain-gauge plethysmography in response to the intraarterial infusion of a subsystemic dose range of L-N-monomethylarginine (L-NMMA), a competitive inhibitor of nitric oxide synthase. In 18 normal subjects, the baseline FBF of 3.6 +/- 1.4 was decreased by 0.3 +/- 0.5 (p < 0.01), 1.0 +/- 0.7 (p < 0.01), 1.4 +/- 0.9 (p < 0.01), and 1.3 +/- 1.3 (p < 0.01) ml/min/100 ml forearm volume during infusions of 1, 4, 8, and 16 mumol/min of L-NMMA, respectively. In 10 patients with heart failure, the baseline FBF of 2.6 +/- 0.9 was decreased by 0.4 +/- 0.5 (p < 0.05), 0.4 +/- 0.5 (p < 0.05), 0.9 +/- 0.8 (p < 0.01), and 0.9 +/- 0.7 (p < 0.01) ml/min/100 ml forearm volume with the 4 doses of L-NMMA, respectively. There was no difference in the L-NMMA response between the 2 groups in terms of absolute flow, percent change, or with analysis of covariance to adjust for different baselines. The stable end products of nitric oxide (nitrite and nitrate) were measured in the forearm venous effluent. Nitrite and nitrate levels at baseline were not reduced in patients with heart failure.(ABSTRACT TRUNCATED AT 250 WORDS)

[Air plethysmography in the diagnosis of primary venous insufficiency of lower extremities]

Through the assessment 101 limbs of 77 subjects by air plethysmography (AP), we studied the method of AP test and the values of various indices in diagnosis of primary venous insufficiency (PVI). Venous filling index (VFI) was found valuable to quantitate the venous reflux with its value beyond the threshold of 5 ml/sec. It has a potential value to assess the effect of operations on PVI, such as valvuloplasty aiming to abolish venous reflux. Ejection fraction (EF) was found to be abnormal with its value less than 40%. It may be used to evaluate the function of calf pump quantitatively, predict the ulcer formation, and help make a decision of surgery timely. The comprehensive analysis of VFI, EF, RVF (residual volume fraction) and AVP (ambulatory venous pressure) indicated that there seems to be different types of PVI: type 1, low ejection (low EF) high venous reflux (high VFI); type 2, high ejection low venous reflux; type 3, low ejection low venous reflux. This new classification may impose some on the selection of adequate therapies, which will be further investigated.

Evaluation of three different techniques used to measure chest wall movements in children

Several techniques exist for assessing chest wall movements in children, that incorporate different measurement principles. Although the output from such devices appears very similar, the comparability of data from different devices needs to be evaluated. We have investigated the simultaneous measurement of chest wall movement using three different devices in 12 children recovering from intensive care. The devices used were inductance plethysmography (assessing thoracic cross-sectional area), magnetometers (assessing thoracic diameter), and a Hall device strain guage (assessing thoracic circumference). Measurements of respiratory timing and of phase angle between rib cage and abdomen in these patients showed a close agreement between devices in ventilated patients. However, occasional inconsistencies occurred in patients who were breathing spontaneously. We suggest that it may not always be appropriate to directly compare data on chest wall movements in children recorded using different measurement techniques. The best method of measurement varies with the clinical picture.

Design and evaluation of a fibre-optic sensor for limb blood flow measurements

A fibre-optic microbending sensor for clinical use in venous occlusion plethysmography (VOP) has been developed. The sensor utilizes the microbending principle to detect the volume expansion of a limb following venous occlusion. This principle is based on the loss of energy in an optical fibre that undergoes mechanical perturbations. A comparative study of 10 healthy subjects has been made between the new fibre-optic sensor and a mercury strain-gauge sensor. Each subject's limb blood flow was recorded 10 times. The two sensor types were positioned closely together on the same limb. The result of the study shows a high correlation (r = 0.949) verifying that the fibre-optic sensor's performance makes it a suitable alternative to the mercury strain-gauge sensor.

Five-electrode field plethysmography technique for separation of respiration and cardiac signals

Respiration monitoring by means of electric field plethysmography is influenced by cardiac activity, which represents an artefact although of physiological relevance itself. For a separation of respiration and cardiac signals, a portable plethysmograph was developed, which uses a fifth electrode in addition to the conventional tetrapolar electrode arrangement. The separation is attained by weighted software subtraction of two detected signals. In a comparative way, three mathematical methods are discussed for the effective determination of individual weighting factors. Results of the practical applications indicate the best results for a method based on Fast Fourier Transformation.

Differentiating rapists and non-offenders using the rape index

Some studies have suggested that phallometrically derived rape indices can differentiate groups of rapists and non-offenders. There are other studies however which cast doubt on this assertion, at least in so far as it applies to all but those few rapists who are sadistic. These studies have used rape indices which are derived from rapists' sexual responses to audiotaped descriptions of mutually consenting sex and brutal sexual assaults. It was hypothesized however, that stimuli which put more emphasis on the degrading and humiliating elements of rape would improve discriminability. Stimuli were compiled to test this hypothesis. The results indicate that neither rape indices derived from the physically brutal elements nor the degrading elements of rape were able to discriminate between rapists and non-offenders. Furthermore, these indices were not related to offence histories. The results are discussed in terms of their implications for the assessment of rapists and theoretical considerations of their behaviour.

Correlation of venous noninvasive tests with the Society for Vascular Surgery/International Society for Cardiovascular Surgery clinical classification of chronic venous insufficiency

PURPOSE

Noninvasive tests for the evaluation of chronic venous insufficiency (CVI) include quantitative photoplethysmography (QPG), air plethysmography, and duplex ultrasonography measurement of valve closure time (VCT). These tests have been shown to accurately identify the presence of CVI, define the disease, and locate the involved segments. However, the correlation of noninvasive assessment of CVI with the clinical severity (Society for Vascular Surgery/International Society for Cardiovascular Surgery staging) has not been addressed critically.

METHOD

During an 18-month period, 74 limbs were prospectively evaluated with clinical examination, air plethysmography, QPG and duplex ultrasonography.

RESULTS

We studied 52 patients with a mean age of 46 years. There were 14 stage 0 limbs, 14 stage 1, 15 stage 2, and 31 stage 3. We found significant differences (p < 0.05) between normal limbs and those with CVI only by VCT and QPG. There were also marked trends toward worsening mean values for reflux (VCT, QPG, and venous filling index) and venous hypertension (residual volume fraction) between stages 0 to 1, and 1 to 2; however, there was a large degree of overlap between all groups. No test discriminated stage 2 from 3. Assessment of calf muscle pump function with ejection fraction showed no difference between any groups.

CONCLUSION

The Society for Vascular Surgery/International Society for Cardiovascular Surgery criteria for CVI staging distinguishes ulcerated limbs (stage 3) from those with nonulcerating skin changes (hyperpigmentation, brawny edema, and subcutaneous fibrosis) (stage 2). However, we were not able to distinguish these groups by available noninvasive methods. This may imply that these tests are not accurate enough or that the progression from lipodermatosclerosis to frank ulceration is not accounted for by large-vessel hemodynamic changes, but rather by microcirculatory alterations.

Outcome of patients with abnormal ocular pneumoplethysmographic measurements undergoing coronary artery bypass grafting

A total of 1780 patients without symptoms of cerebral ischemia undergoing coronary artery bypass grafting (CABG) were screened before surgery for carotid stenosis by pneumophlethysmography. An abnormal test was defined as a difference in ophthalmic artery pressures of > or = 5 mmHg or ophthalmic-brachial pressure index < or = 0.69. Some 99 patients (5.6%) had an abnormal ocular pneumoplethysmographic measurement (89 unilateral, ten bilateral). Of these, 26 patients underwent prophylactic carotid endarterectomy before CABG (group 1), while the remaining 73 patients had reconstruction without previous carotid endarterectomy (group 2). A total of 100 patients (group 3) with normal ocular pneumoplethysmographic results were used as controls. The three groups were comparable with respect to age, diabetes, hypertension, smoking and severity of coronary artery disease. Early (30-day) postoperative stroke rates were 0 and 4% (n = 3) for groups 1 and 2 respectively, and 0% for group 3 (P > 0.07). Early mortality rates after CABG for groups 1 and 2 were 4% (n = 1) and 1% (n = 1), respectively and 2% (n = 2) for groups 3 (P > 0.4). Late follow-up (mean 48 months) demonstrated stroke rates of 0% for group 1, and 10% and 4% for groups 2 and 3 (P > 0.08). The early mortality and stroke rates in the ten patients with bilateral abnormal ocular pneumoplethysmographic values were 0 and 0%. However, late strokes occurred significantly more often (43%) in patients with bilateral abnormal results compared with those with unilateral abnormal findings when both groups did not undergo carotid endarterectomy (P < 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)

Chest wall motion in neonates utilizing respiratory inductive plethysmography

After calibration, respiratory inductive plethysmography can accurately measure breathing patterns noninvasively by transmitting ribcage and abdomen compartment changes caused by ventilation through oscillator circuitry. We measured the breathing pattern of nine quietly awake healthy newborn infants and assessed components reflecting asynchrony, paradoxic motion, and overall phasic relations between ribcage and abdomen compartments. Breathing pattern data (mean +/- SD) on 136 total tidal volume (Vt) breaths revealed: Vt, 14.4 +/- 3.40 ml; frequency, 52.1 +/- 11.5 beats/min; ribcage contribution to Vt, 32.2% +/- 13.4%; maximum compartmental amplitude/Vt, 1.01 +/- 0.01; phase angle, 13.2 +/- 9.50 degrees; inspiratory asynchrony index, 0.26 +/- 0.20 ml2/ml; expiratory asynchrony index, 0.42 +/- 0.3 ml2/ml; and average asynchrony index, 0.34 +/- 0.20 ml2/ml. Results demonstrated a high degree of synchrony between ribcage and abdomen movement during quietly awake breathing. Outward motion of the abdomen preceded that of the ribcage for almost every measured breath.

[Functional venous explorations]

The methods for exploring venous function globally are presented first. These methods include venous pressure and plethysmography for which the methods using a garrot are separated from those using air volumetry which give reliable physiological and reproducible results. The Nachev method, the thermometry, the thermography and isotope clearances are also reviewed since they have been important in the development of exploration of venous function. The methods giving morphological or segmentary data are then presented in historical order: phlebography (completed by tomodensitography and nuclear magnetic resonance), then ultrasonography with Doppler, echography and duplex and colour techniques. Finally promising methods for the future including oxygen partial pressures, laser-Doppler, capillaroscopy and venous endoscopy are discussed. For each method, there is a description of the technique, a presentation of the measured parameters and their reliability, the signification of the measurement and its clinical use. Finally, each method is discussed in the context of concrete clinical situations with a schema for management of diagnosis.

[Drug treatments of chronic venous insufficiency: pharmaco-clinical evaluation]

There are many methods for the assessment of venotropic drugs. Clinical trials based on randomized comparison with placebo are essential. The different methodes used for the evaluation of the functional effects are chosen on the basis of their performance and pertinence for the study objectives. These include three aims which we feel are essential: increased venous tone, decreased capillary permeability and reversal of microcirculatory impairment. Calf plethysmography is highly adapted for the evaluation of venous tone. The mercury gauge works well, but the future will tell if air plethysmography is more adapted here. For capillary permeability, fluoresceine angioscopy is without a doubt the most sensitive and specific method. Unfortunately many laboratories do not have this equipment. If it is not available, the suction cup test or the Landis isotope test may be used although these tests have their limits. For impaired microcirculation, the most interesting test is the laser-Doppler; the results are well correlated with the severity of the chronic venous insufficiency and return to normal after treatment. TcPO2 and capillaroscopic measurements are less sensitive, but are useful in severe cases. Other investigations may be important in individual cases depending on the impact of the medication under study. Drug-induced serum fibrinolytic activity can be measured by the euglobulin lysis time. A haemorheologic effect can be assessed with routine assays (Haematocrit, serum fibrinogen) and measured with tests of red cell deformability and erythrocyte agreggation capacity.

The effect of iloprost in patients with rest pain

Thirty-four patients with ischaemic rest pain in 42 limbs and ankle pressure equal to or less than 50 mmHg have been treated with intravenous infusion of synthetic prostacyclin (iloprost) for eight days. Leg blood flow was measured with air plethysmography before treatment, on day 4 and day 8 of treatment. Total relief of pain for at least 6 weeks occurred in 91% of patients with leg blood flow > or = 40 ml/min, in 18% with leg flow 30-39 ml/min and in 11% with leg flow < 30 ml/min. Complete relief of pain for at least 6 weeks occurred in 92% of patients in whose limbs the blood flow on day 8 was greater than 50 ml/min but only in 6% with blood flow less than 50 ml/min. These results indicate that iloprost increases leg blood flow and that patients likely to respond can be identified from the baseline air plethysmographic measurement of leg blood flow.

Noninvasive blood flow tests in vascular disease

Noninvasive testing is now routine for assessing vascular conditions. Many noninvasive tests are available for obtaining physiologic and anatomic information that is both precise and reproducible. This paper discusses noninvasive testing with plethysmography, Doppler ultrasonography, and duplex scanning for carotid artery occlusive disease, deep venous thrombosis, and peripheral arterial occlusive disease.

Ventilatory pattern during bronchial histamine challenge in asthmatics

We wanted to investigate whether asthmatic subjects change their ventilatory pattern consistently when forced expiratory volume in one second (FEV1) has declined by at least 20% during bronchial histamine challenge, in order to assess whether respiratory pattern analysis can be used to monitor bronchial obstruction continuously. Histamine challenge was performed twice within a four week period, in eight asthmatic teenagers. Respiratory inductive plethysmography (RIP) was used for respiratory pattern evaluation, whilst the patients breathed on a mouthpiece attached to a pneumo-tachometer (PTM) whilst wearing a noseclip (first histamine challenge), and during natural breathing (second HiCh). End-tidal carbon dioxide tension (PETCO2) was measured on both occasions. During the second histamine challenge, four of the eight patients responded with a 72% (mean) increase in minute ventilation (VE), an 80% increase in mean inspiratory flow (VI), and a 20% decrease in PETCO2. VE and VI were unchanged, or tended to decrease, among the other four patients (ventilatory nonresponders). Neither provocative dose producing a 20% fall in FEV1 (PD20) to histamine nor the magnitude of the fall in FEV1 differed between ventilatory responders and nonresponders. The ventilatory response to inhaled histamine was abolished when breathing through a PTM. Histamine induced bronchospasm is not uniformly reflected in the breathing pattern. Hyperventilation during histamine challenge might be the consequence of vagal airway receptor activation. Respiratory pattern analysis is not a feasible way to monitor bronchial obstruction during histamine challenge.