Assessment of SPECT ventilation-perfusion imaging in patients with lung cancer

Ventilation and perfusion SPECT images during tidal breathing were studied in 15 cases of lung cancer using ^81mKr gas and ^99mTc-microspheres. Furthermore, functional images of V/Q ratio and Q/V ratio were prepared, and their clinical significance is descussed with reference to general lung function. There was a decreas in %VC and %FEV _1.0in 7 of 15 cases, and an increase of AaDo₂ in the blood gas analysis in 12 of 15 cases. Both planar and SPECT images showed ventilation and perfusion abnormalities in all 15 cases. Of these, 12 patients showed matched ventilation and perfusion defects, 2 patients a dead-space effect and 1 patient a shunt effect. In comparing planar and SPECT images, depiction of ventilation and perfusion impairments were equally clear in 11 cases, but in 3, showing a lobar or segmental defect with a shunt effect, the SPECT images were superior. In a patient with markedly impaired function of the affected lung, the remaining function could not be depicted by SPECT. From the above, it seems that better information can be obtained for understanding the ventilation and perfusion states of lung cancer by adding the SPECT images to the planar image.     

Oesophageal atresia: caudo-thoracic epidural anaesthesia reduces the need for post-operative ventilatory support

The mortality of neonates with oesophageal atresia in the Third World remains high because of delays in presentation and diagnosis. Lack of appropriate intensive care facilities is a further contributing factor. Caudothoracic epidural anaesthesia was used during surgical repair of oesophageal atresia in 35 patients in an attempt to minimise the need for post-operative ventionally support. This group was compared with 36 patients whose surgery was performed under general anaesthesia. The age at the time of referral, sex ratio, and weight were comparable in both groups. Using the Waterson classification, a greater number of poorer prognostic patients were seen in the epidural group (P <0.02). In all Waterson risk categories fewer patients required ventionally support post-operatively, which was statistically significant (P <0.01) when all categories were combined. We are encouraged by our results and believe this technique has a rôle in the management of neonates undergoing major surgery, both where neonatal intensive care exist or is deficient as in many parts of the Third World.     

Reproducibility of the parameters of the on-transient cardiopulmonary responses during moderate exercise in patients with chronic obstructive pulmonary disease

To be clinically useful as indices reflective of altered physiological function consequent to interventions in patients with chronic obstructive pulmonary disease (COPD), the time constant (τ) and steady-state amplitude of the kinetic responses for oxygen uptake ( ) carbon dioxide output ( ) ventilation ( ) and heart rate (HR) have to be appropriately differentiable and reproducible. We therefore assessed the reproducibility of τ and steady state amplitude values in 41 patients with severe COPD [mean (SD)] [forced expiratory volume in 1 s=41 (7)% predicted], aged 64 (5) years. Of the total, 6 of the patients (15%) did not produce breath-by-breath data of sufficient quality to warrant kinetic analysis. The remaining 35 patients completed two moderate-intensity 10 min square-wave exercise tests separated by 2 h, both before and after an endurance training programme. Tests were conducted on an electromagnetically-braked cycle ergometer at an exercise intensity corresponding to 80% of the estimated lactate threshold (θ_La) or 50% of peak oxygen uptake if θ_La was insufficiently differentiable. Breath-by-breath measurements of , , and HR were averaged into 10 s bins and the on-transient response kinetics were estimated using a mono-exponential model. Analysing the pre-training and the post-training test 1 and test 2 comparisons together, the test 1 –test 2 differences were not significantly different from 0 for either τ or A. The standard deviation of the test 1 –test 2 differences allowed us to define the magnitude of change that would reach statistical significance. For τ, this averaged some 8, 10, 11 and 8 s, for , , and HR, respectively, for a one-tailed paired-comparisons test (i.e. appropriate for assessing hypothesised improvements resulting from an intervention); for a two-tailed comparison, the differences were approximately 2 s greater. The corresponding one-tailed values for A were 100 ml·min^–1, 95 ml·min^–1, 2.5 1·min^–1 and 4 beats·min^–1, respectively; the two-tailed values were 10%–15% greater. We therefore conclude that both τ and A for moderate-intensity exercise can be reproducibly estimated in patients with COPD when the data set provides a sufficiently large amplitude of response and sufficiently low sample variability to allow appropriate parameter estimation. Electronic Publication     

Effect of sleep deprivation on tolerance of prolonged exercise

Summary Acute loss of sleep produces few apparent physiological effects at rest. Nevertheless, many anecdotes suggest that adequate sleep is essential for optimum endurance athletic performance. To investigate this question, heavy exercise performance after 36 h without sleep was compared with that after normal sleep in eight subjects. During prolonged treadmill walking at about 80% of the max, sleep loss reduced work time to exhaustion by an average of 11% (p=0.05). This decrease occurred despite doubling monetary incentives for subjects during work after sleeplessness. Subjects appeared to fall into “resistant” and “susceptible” categories: four showed less than a 5% change in performance after sleep loss, while four others showed decrements in exercise tolerance ranging from 15 to 40%. During the walk, sleep loss resulted in significantly greater perceived exertion (p<0.05), even though exercise heart rate and metabolic rate ( and ) were unchanged. Minute ventilation was significantly elevated during exercise after sleep loss (p<0.05). Sleep loss failed to alter the continuous slow rises in _E and heart rate that occurred as work was prolonged. These findings suggest that the psychological effects of acute sleep loss may contribute to decreased tolerance of prolonged heavy exercise. Supported in part by Public Health Service grant PHS S07 RR 5371, and by Grant DAMD-17-81-C-1023 from the U.S. Army     

Effects of ventilatory pattern on exhaled nitric oxide in mechanically ventilated rabbits

BACKGROUND: Nitric oxide [NOexp] is present in exhaled air in many species. During experiments on pressure-controlled inverse ratio ventilation (PCIRV) in rabbits, increased [NOexp] was observed during PCIRV. The present study was undertaken to clarify which component of PCIRV increased [NOexp]. METHODS: Three groups of six New Zealand White rabbits were anaesthetised and mechanically ventilated. Exhaled nitric oxide, lung mechanics and gas exchange were measured using an experimental protocol designed to assess the effects of variations in 1) flow profile, 2) inspiratory time and 3) time-weighted tidal volume. Ventilator settings used were volume and pressure control ventilation at I:E ratios of 1:2 and 4:1. RESULTS: Constant and decelerating flow gave comparable [NOexp] levels (20.0 +/- 6.4 vs. 21.9 +/- 7.7 ppb, n.s.) when time-weighted tidal volume was kept constant. Using conventional (I:E 1:2) or inverted (I:E 4:1) I:E ratios in combination with decelerating flow and constant time-weighted tidal volumes did not alter [NOexp] (26.0 +/- 3.6 vs. 24.0 +/- 5.8 ppb, n.s.). An increased time-weighted tidal volume produced by pressure control with an I:E ratio of 4:1 increased [NOexp] (29.6 +/- 7.4) in comparison to constant (19.3 +/- 4.1, P < 0.05) and decelerating flow ventilation (19.6 +/- 3.6, P < 0.05) with I:E ratios of 1:2. CONCLUSION: The exhaled NO concentration was affected by ventilator setting. Increased levels of [NOexp] were observed with increases in time-weighted tidal volume, whereas changes in flow pattern and inspiratory time did not seem to influence airway NO production or release.     

Regulation of PaCO2 during rest and exercise: A modeling study

A nonlinear mathematical model of the CO₂ control system was used to examine a number of issues concerning the regulation of PaCO₂ during rest and exercise. To gain insight to the regulatory properties of the respiratory system, the open loop gain (G_l) and closed loop sensitivities S_i=ξPaCO₂/ξPiCO₂ and were calculated. Gl indicates the ability of a control system to regulate the controlled variable, PaCO₂ in the model. Si and Sv represent the change in PaCO₂ to unit changes in PiCO₂ and , respectively. Model predications were obtained for rest and various intensities of exercise for the following challenges to the respiratory system: (a) CO₂ inhalation, (b) i.v. CO₂ loading, (c) application of an external dead space, and (d) a shift in the resting operating point. Increasing exercise intensity produced a substantial decrease in Gl and increase in Si consistent with the hypothesis that exercise degrades the ability of the respiratory system to regulate PaCO₂. However, Sv decreased indicating that the respiratory system would actually be better able to regulate PaCO₂ if there were fluctuations in . Thus, Gl does not completely describe the regulatory characteristics of the respiratory control system. It is demonstrated that the regulatory characteristics of the respiratory system as described by Gl, Si, and Sv are complex and depend on the nature of the challenge. Techniques for systematically describing the regulatory properties of the CO₂ control system are described.     

Modelling the dynamic ventilatory response to hypoxia in humans

A two-component dynamic model was used to describe the ventilatory response to sustained hypoxia in humans. One component (X_s) represents the stimulating effects of hypoxia and the other component (X_d), the hypoxic ventilatory decline. The total ventilatory response to hypoxia is represented by the sum of the two components. A nonlinearity is included to account for the nonlinear steady-state ventilatory response to hypoxia. A sensitivity analysis of the model indicates that, with a step change in as the input, all the parameters can be estimated from the data except for the nonlinearity. The relative sensitivity of the parameters from the model analysis was confirmed in an experimental study. However, comparing steps into hypoxia versus steps out of hypoxia we found a decrease in the gains of both components. The most likely explanation for the decrease in the gains is that the combination of X_s and X_d is not entirely additive. Other models may be required to completely describe the ventilatory response to inputs more complex than steps.