Factors influencing pulsus paradoxus in asthma

Respiratory Fluctuation of Peak Systolic Velocities in the Carotid Doppler Waveforms of Patients With Obstructive Airway Disease: Evidence of Pulsus Paradoxus With Experimental Validation

OBJECTIVES

To characterize fluctuations in peak systolic velocities (PSVs) in Doppler waveforms of the carotid artery in patients with and without obstructive airway disease and in volunteers subjected to incremental levels of airway resistance in an experimental model.

METHODS

The PSV variation in common carotid waveforms was measured in 100 patients who had had a carotid ultrasound examination and no respiratory or carotid disease. This was compared to that of patients who had this study during an admission for acute exacerbation of chronic obstructive pulmonary disease (COPD). The PSV variation was correlated with pulmonary function testing. In addition, 14 healthy volunteers were asked to breathe through 5 resistors. Simultaneous recordings were made of Doppler waveforms in the common carotid artery, cardiac activity, and respiration. Peak systolic velocity changes from inspiration to expiration were calculated.

RESULTS

Of the 100 patients without respiratory disease, the magnitude of the PSV variation averaged 6.3 cm/s. Of the 33 patients with COPD, the PSV variation averaged 16.5 cm/s. Nineteen of the 33 patients with COPD had concurrent pulmonary function testing; there was a statistically significant correlation between the PSV variation and forced vital capacity and forced expiratory volume indices. For the volunteers, mean velocity changes were 7.1, 6.6, 8.3, 15.1, and 16.1 cm/s for 0.00-, 2.15-, 3.27-, 3.58-, and 5.77-cm H₂ O/L/s levels of breathing resistance, respectively. There was a statistically significant relationship between an increasing airway load and the decline in PSV during inspiration (P = .02).

CONCLUSIONS

The PSV variation is greater in patients with increased airway resistance. Similar changes are evident in volunteers breathing into resistors. These findings likely reflect pulsus paradoxus.

A new noninvasive method for measurement of dynamic lung compliance from fluctuations on photoplethysmography in respiration

Lung compliance is important in interstitial lung disease (ILD). However, the measurement requires placement of an esophageal pressure probe and is therefore not done in routine clinic practice. This study was performed to develop and verify a new noninvasive method for estimation of dynamic lung compliance (Cdyn) with a photoplethysmograph (PPG) of pulse wave represented as the changes of absorbance of green LED for hemoglobin and to examine its usefulness. A system for measuring Cdyn in combination with changes in estimated pleural pressure (Ppl) from the fluctuations on PPG with respiration and lung volume measured simultaneously by spirometry was developed and verified to show correspondence with the estimated Ppl and the esophageal pressure (Pes), estimated Cdyn, and Cdyn measured with an esophageal balloon. Furthermore, the estimated percentage of predicted Cdyn (%Cdyn) was compared among healthy subjects (HS) (n = 33) and patients with chronic obstructive pulmonary disease (COPD) (n = 31) and ILD (n = 30). Both estimated Ppl and Cdyn were significantly correlated with Pes (r = 0.89) and measured Cdyn (r = 0.63), respectively. The estimated %Cdyn in ILD showed significantly lower values than those in HS and COPD. The estimated %Cdyn was significantly related to percentage of predicted vital capacity (VC) (r = 0.57, P < 0.01) and percentage of predicted diffusion capacity of carbon monoxide (Dl_CO) (r = 0.50, P < 0.01) in patients with ILD. These findings suggested that the newly developed noninvasive and convenient method for Cdyn estimation using a combination of PPG and spirometry may be useful for the assessment of lung fibrosis in ILD.NEW & NOTEWORTHY Our newly developed method for measuring dynamic lung compliance (Cdyn) in combination with changes in estimated intrathoracic pressure from fluctuations on photoplethysmography with respiration and lung volume measured simultaneously by spirometry showed good linear regression between the estimated Cdyn and the Cdyn measured with an esophageal balloon, and the estimated percentage of predicted Cdyn (%Cdyn) showed significantly lower values in patients with interstitial lung disease (ILD) than in healthy subjects and chronic obstructive pulmonary disease (COPD) patients and significant correlations with vital capacity and lung diffusion capacity.

Acute severe asthma

Acute severe asthma remains a major economic and health burden. The natural history of acute decompensations is one of resolution and only about 0.4% of patients succumb overall. Mortality in medical intensive care units is higher but is less than 3% of hospital admissions. "Near-fatal" episodes may be more frequent, but precise figures are lacking. However, about 30% of medical intensive care unit admissions require intubation and mechanical ventilation with mortality of 8%. Morbidity and mortality increase with socioeconomic deprivation and ethnicity. Seventy to 80% of patients in emergency departments clear within 2 hours with standardized care. The relapse rate varies between 7 and 15%, depending on how aggressively the patient is treated. The airway obstruction in the 20-30% of people resistant to adrenergic agonists in the emergency department slowly reverses over 36-48 hours but requires intense treatment to do so. Current therapeutic options for this group consist of ipratropium and corticosteroids in combination with beta2 selective drugs. Even so, such regimens are not optimal and better approaches are needed. The long-term prognosis after a near-fatal episode is poor and mortality may approach 10%.

Mechanisms of Cough Syncope as Evaluated by Valsalva Maneuver

Successful treatment of cough syncope depends on the correction of various pathogenetic mechanisms among different patients. The valsalva maneuver (VM), which elicits hemodynamic responses mimicking coughs, has potential for investigating the individual pathogenesis of cough syncope. Eighteen consecutive patients suffering from cough-induced syncope were examined. All patients were asked to cough and to perform VM several times under continuous cerebral blood-flow velocity and blood pressure (BP) monitoring by transcranial Doppler and finger plethysmography. Eight patients demonstrated abnormal VM characterized by the absent BP overshoot following the relief of straining. Patients demonstrating abnormal VM had delayed BP recovery after cough (median, 16.4; range, 8.7-25.6 seconds) compared to those demonstrating normal VM (2.6, 1.3-3.8 seconds, p < 0.001). Seven of the 10 patients exhibiting normal BP overshoot during VM had stenotic arterial lesions in the cerebral or coronary circulation, whereas only one of the eight patients demonstrating absent BP overshoot had coronary artery disease (70% vs. 12.5%, p = 0.025). Other clinical profiles, body mass index, frequency of obstructive pulmonary disease and valsalva ratio did not differ between patients featuring normal and absent BP overshoot. In conclusion, the pathogenesis of cough syncope could be different between patients with normal and abnormal VM responses. Patients who had no BP overshoot during VM sustained prolonged hypotension after cough. The VM helps in discriminating among pathogenic mechanisms and guiding investigation and treatment for cough syncope patients.

Pulsus paradoxus: an objective measure of severity in croup

We used a noninvasive monitor of arterial pressure to determine the utility of pulsus paradoxus (PP) as an objective severity measure in croup. We performed a prospective, blinded comparison of PP in children with croup versus healthy control subjects, analyzed the relationship between PP and Westley croup score (WCS), and observed the effect of racemic epinephrine (RE) on PP and WCS in a subgroup of patients with severe croup. The PP and WCS were measured at presentation and in severe patients after treatment with RE. Mean PP was 6.1 +/- 1.8 (SD) mm Hg (n = 29) in control subjects compared with a mean of 17.8 +/- 11.2 (SD) mm Hg (n = 28) in patients with croup (p < 0.00001). There was significant concordance between baseline WCS and PP (Spearman's rho: 0.68; p = 0.0001). The mean decrease in PP after RE was 7.5 +/- 11.8 (SD) mm Hg (p = 0.05; n = 12). The magnitude of decrease in PP after RE has significant concordance with the concurrent decrease in WCS (Spearman's rho: 0.73; p < 0.007). PP is elevated in children with croup, and the magnitude of elevation correlates with severity as measured by the WCS. PP may have utility as a research tool to objectively measure the severity of upper airway obstruction in croup.

Continuous noninvasive determination of pulsus paradoxus: a pilot study

OBJECTIVE

To evaluate two methods of continuous, noninvasive monitoring of pulsus paradoxus (PP).

METHODS

A single-subject, nonblind assessment was conducted of the ability of noninvasive monitoring techniques to measure experimentally induced PP. Variable degrees of PP were induced in a healthy adult breathing through a one-way valve to which a series of external airway resistances were added. Intra-arterial pressure (IAP), finger arterial blood pressure (FINAP), pulse oximeter pulse waveform, and chest wall motion were continuously recorded. For each resistance, PP was calculated from the IAP (PPIAP) and the FINAP (PPFINAP) recordings. PP was measured manually (PPmanual) in the opposite arm. The percentage pulse waveform decrease on inspiration (%PWDpleth) was derived from the oximeter pulse waveform. These measurements were compared with the PPIAP. Bias was assessed as the mean difference between PP measures.

RESULTS

PPFINAP was highly correlated with PPIAP (r = 0.96; 95% CI 0.93 to 0.98; p < 0.0001). There was a weak correlation between PPmanual and PPIAP (r = 0.27; 95% CI -0.05 to 0.55; p = 0.0963). The %PWDpleth correlated with PPIAP (r = 0.59, 95% CI 0.32 to 0.78; p = 0.0002). Bias was -1.515 +/- 5.6 mm Hg between PPIAP and PPFINAP; and -4.508 +/- 23.4 mm Hg between PPIAP and PPmanual.

CONCLUSION

An accurate and continuous PP can be measured noninvasively using a FINAP monitor. This method has much better agreement with IAP measurements than do manual measurements. The qualitative information provided by the oximeter pulse waveform is less accurate than that provided by the FINAP monitor, but is a potentially useful screening tool for detection of significant PP.

Cardiovascular effects of airways obstruction

Airways obstruction is usually associated with substantial decreases in inspiratory and mean intrathoracic pressure (ITP). The change in ITP is correlated with the degree of inspiratory fall in arterial pressure, pulsus paradoxus. The factors influencing the degree of pulsus include venous return, afterload effects on the left ventricle (LV), diastolic ventricular interdependence, lung volume, and circulatory reflexes. I have reviewed these factors and attempted to demonstrate that their relative importance changes under different circumstances. I have discussed the importance of measuring transmural pressures to assess ventricular performance, and pointed out some possible pitfalls in the use of esophageal or pleural pressure to estimate LV surface pressure. During normal and loaded inspiration, decreased LV preload, probably related to right ventricle (RV)-LV diastolic interdependence, appears to be the primary mechanism responsible for decreased stroke volume during inspiration. During Mueller maneuvers, and possibly with severe decreases in ITP. LV afterload may be more important. When lung volume increases, as with asthma, venous return from the lower body may be a more important determinant of pulsus paradoxus. Although previous predictions that decreased ITP would lead to increased myocardial O2 consumption were not borne out, coronary blood flow did increase with inspiratory loading. This appears to be due to a nonvagally mediated change in autonomic tone with loaded breathing. This and other reflex-mediated effects deserve more attention in future studies of stressed or abnormal inspiration. As a final point, pericardial tamponade probably leads to pulsus paradoxus by exaggerating normal diastolic right-left interactions.

Decreased paradoxic pulse from increased venous return in severe asthma

During severe asthma, paradoxic pulse may result from increased impedance to left ventricular ejection, mechanical impairment of left ventricular filling by ventricular interdependence or decreased pulmonary venous return augmented by hypovolemia. We studied the effect of reversible blood volume expansion by MAST inflation during severe attacks of asthma. Ten patients with clinically detectable paradoxic pulse of more than 20 mm Hg were studied. All had a history of reversible bronchial asthma with evidence of respiratory and circulatory failure. Standard therapy for asthma was started. We observed no difference in respiratory and heart rates during MAST inflation. Paradoxic pulse was consistently decreased during MAST inflation; paradoxic pulse returned to baseline values after MAST deflation. The decrease in paradoxic pulse was produced by an increased inspiratory systolic arterial pressure. We conclude that a reduction in pulmonary venous return is more important than ventricular interdependence in producing paradoxic pulse during severe asthma.

Cardiovascular response to acute airway obstruction and hypoxia

We wished to evaluate the role of hypoxia in the production of cardiovascular manifestations of acute airway obstruction. We monitored blood pressure, electrocardiogram, and radionuclide ejection fraction in 14 healthy volunteers on exposure to four experimental conditions: expiratory resistive loading while breathing room air (RAL), expiratory resistive loading while hypoxic (HL), hypoxia alone (H), and expiratory resistive loading while voluntarily hyperventilating in a pattern similar to HL trials (VL). Mean respiratory-related oscillation in systolic blood pressure (pulsus paradoxus) increased significantly under each experimental condition compared with those at baseline (2 +/- 2.3 mm Hg): for RAL, 21 +/- 8.4 mm Hg; for HL, 34 +/- 16.3 mm Hg; for H, 10 +/- 5.4 mm Hg; for VL 26 +/- 13.4 mm Hg. Pulsus paradoxus was significantly greater under conditions of moderate hypoxia (saturation, 80%) than of mild hypoxia (saturation, 90%). Electrocardiographic changes were more marked under HL and H conditions than under RAL and VL conditions. HL induced changes in blood pressure and frontal QRS axis that were qualitatively similar to those seen in naturally occurring asthma. Radionuclide ejection fraction showed no dramatic change with any experimental condition. We conclude that hypoxia magnifies the cardiovascular changes induced by acute expiratory resistive loads and may contribute to the degree of pulsus paradoxus seen in severe asthma.

Mechanism of decreased left ventricular stroke volume during inspiration in man

Radionuclide ventriculography was performed in 15 healthy subjects during quiet breathing and during inspiration against a 24 cm H2O threshold load with a respiratory gating technique. Inspiratory threshold loading caused an inspiratory decrease in ejection fraction from 64% to 59% (p less than .001). Stroke counts proportional to stroke volume decreased by 9.6% (p less than .02) due to an increase in end-systolic counts of 15.9% (p less than .05). End-diastolic counts decreased in four subjects and increased in three subjects, but the mean counts did not change significantly. These findings suggest that negative pleural pressure causes an impediment to left ventricular ejection comparable to an increase in arterial pressure. Respiratory gating of radionuclide ventriculography during loaded breathing is suggested as a controlled stress on the ventricle for diagnostic purposes.

Effect of negative pleural pressure on left ventricular hemodynamics

Negative pleural pressure alters left ventricular (LV) function. LV volume changes have been studied in human subjects, but little is known of the hemodynamic effects. The effect of changes of pleural pressure on LV hemodynamics during a Mueller maneuver (inspiration against an obstruction) was studied in 11 subjects and during quiet, unobstructed inspiration in 3. During the Mueller maneuver, there was an initial decrease in pulmonary wedge pressure and aortic systolic pressure, almost as great as the decrease in pleural pressure. Thereafter, these pressures increased despite a sustained reduction in pleural pressure. Toward the end of the Mueller maneuver, pulmonary wedge transmural pressure averaged 31 +/- 12 mm Hg and in 6 patients large v waves developed. The increase in aortic transmural pressure averaged 30 +/- 16 mm Hg. Aortic pulse pressure decreased on the first beat from control levels of 59 +/- 21 to 47 +/- 21 (p less than 0.001) and then returned to control levels. During normal breathing in 3 subjects, studied with intraesophageal balloons, there was a similar increase in both transmural aortic and transmural pulmonary wedge pressures with a decrease in pleural pressure 6 mm Hg during inspiration. Thus, increased negative pleural pressure was associated with a marked increase in pulmonary wedge transmural pressure; the increase was approximately proportionate to the decrease in pleural pressure. It is suggested that this increase was due to increased impedance to LV ejection and to right ventricular expansion interfering with LV diastolic filling.

Evaluation and management of acute asthma

Successful management of asthma requires an expectant, aggressive approach to asthma attacks as well as a careful management program to maintain remissions. The patient must recognize when he or she needs help, and the physician must be able to assess the severity of deterioration and provide rapid aggressive care. Failures are usually due to patient or physician error, or both. These relate to failures both outside and inside the hospital. Once inside the hospital, failure is mainly the responsibility of the physician. It is clear that deaths in the hospital have been associated with inadequate patient observation and monitoring, and treatment that is less aggressive than required. With appropriate patient and physician education and aggressive management, deaths during acute asthma attacks should be rare.