Numerical analysis of pressure and flow pulsations in a segment of the arterial tree

The arterial blood pressure and the rate of volume pulsations were measured experimentally as functions of time for a segment of the human arm. Using these curves and a type of identification program, common in control engineering, a mathematical model was calculated for the arterial tree included in the segment. This mathematical model led to the construction of an electrical analogue circuit for simulating the time-dependence of the rate of volume pulsations on the arterial pressure. In both cases the results show a close agreement between the simulated curves and the physiological curves determined experimentally. The inertia of blood and vessels is shown to be negligible, while non-linear compliances must be included when dealing with wide pressure ranges.     

Effect of prenatal heat stress on brain growth and serial discrimination reversal learning in the guinea pig

Exposure of pregnant guinea pigs to an environmental temperature of 42°C for 1 hr daily on Days 20–24 of gestation resulted in a significant reduction in the birthweight and brainweight of newborn offspring. These deficits persisted to early maturity and were still evident at 250 days of age following behavioral testing. Although some degree of postnatal neurogenesis and brain growth had occurred, this was not sufficient to compensate for the retarding influence of prenatal hyperthermia. Heat stress was also observed to seriously impair learning performance on the original discrimination task and this tendency persisted over the subsequent 4 reversals for both initial and perseverative errors. Impaired learning performance was related to reduction in brainweight. Animals with lower brainweights made significantly more initial, perseverative and total number of errors over the 5 problems. In addition, 12 of the 14 behaviorally tested stressed progeny had brainweights that were at least 2 standard deviations below the mean of the controls and as a result were classified as micrencephalic. Although heat stressed animals showed a significant reduction in the number of amacrine synapses in the inner plexiform layer of the retina, performance differences were not attributed to changes in synaptic organisation of the retinal circuitry or to visual or other ophthalmic defects, but brain function. Animals with higher mean maternal poststressing core temperatures gave birth to progeny which had smaller whole and part wet-brainweights. Examination of the effect of poststressing core temperature on brainweight revealed that brain growth, independent of bodyweight, was retarded when this temperature elevated above 41.5°C. This represented a rise of approximately 2.1°C above normal and for each 1°C rise above this temperature, brainweight was reduced by 0.4227 g of the control value. Analysis of the atmospheric content of the incubator during stressing sessions ruled out the possibility that changes in level of oxygen and carbon dioxide may have contributed to the retarding influence on fetal development and learning ability in the guinea pig.     

Marrow transplantation in treatment of children with aplastic anaemia or acute leukaemia.

Seventy-six patients, aged 2 to 17 years, were treated with bone marrow transplantation for severe aplastic anaemia or acute leukaemia refractory to conventional therapy. 16 of the 22 patients (73%) who received marrow transplantations for aplastic anaemia are surviving, 12 of these for over one year. In acute leukaemia, using preparation with cyclophosphamide and total body irradiation, 8 of 33 patients (24%) receiving allogeneic and 5 of 8 (63%) receiving syngeneic transplantations are continuing in remission from 3 months to beyond 2 years. The longest continuing remission off therapy is now over 4 1/2 years after preparation with total body irradiation. The major causes of failure remain graft-versus-host disease, infection, graft rejection (aplastic anaemia), and leukaemic relapse.     

Letter to editor

European Journal of Nuclear Medicine and Molecular Imaging -     

Re-inspiration of CO<Subscript>2</Subscript> from ventilator circuit: effects of circuit flushing and aspiration of dead space up to high respiratory rate

Introduction  

Dead space negatively influences carbon dioxide (CO₂) elimination, particularly at high respiratory rates (RR) used at low tidal volume ventilation in acute respiratory distress syndrome (ARDS). Aspiration of dead space (ASPIDS), a known method for dead space reduction, comprises two mechanisms activated during late expiration: aspiration of gas from the tip of the tracheal tube and gas injection through the inspiratory line - circuit flushing. The objective was to study the efficiency of circuit flushing alone and of ASPIDS at wide combinations of RR and tidal volume (V_T) in anaesthetized pigs. The hypothesis was tested that circuit flushing and ASPIDS are particularly efficient at high RR.     

Effect of inspired oxygen fraction on alveolar derecruitment in acute respiratory distress syndrome

Objective High fractions of inspired oxygen (FIO₂) used in acute lung injury (ALI) may promote resorption atelectasis. The impact of derecruitment related to high FIO₂ in ALI is debated. We evaluated derecruitment with 100% vs. 60% FIO₂ at two levels of positive end-expiratory pressure (PEEP).Patients Fourteen consecutive patients with ALI were studied.Interventions Recruited volume at two PEEP levels was computed from two pressure-volume curves, recorded from PEEP and from zero end-expiratory pressure, using the sinusoidal flow modulation method. PEEP-induced recruitment was measured during prolonged expiration as the difference between the two curves at a given pressure. PaO₂/FIO₂ was also measured. PEEP was 5 ± 1 or 14 ± 3 cmH₂O and FIO₂ was 60% or 100%, yielding four combinations. We looked for differences between the beginning and end of a 30-min period with each combination.Measurement and results With low PEEP and 100% FIO₂, recruited volume decreased significantly from 68 ± 53 to 39 ± 43 ml and PaO₂/FIO₂ from 196 ± 104 to 153 ± 83 mmHg. With the three other combinations (low PEEP and 60% FIO₂ or high PEEP and 60% or 100% FIO₂) none of the parameters decreased significantly.Conclusion In mechanically ventilated patients with ALI the breathing of pure oxygen leads to derecruitment, which is prevented by high PEEP.Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.This article is discussed in the editorial available at:     

Elastic pressure-volume curves of the respiratory system reveal a high tendency to lung collapse in young pigs

Objective: To study pressure-volume (P/V) curves over a wide pressure and volume range in pigs.¶Design: Dynamic and static P/V curves (P_dyn/V and P_st/V) and compliance of the respiratory system were studied. The effects of recruitment, positive end-expiratory pressure (PEEP) and body position were analysed.¶Setting: Research animal laboratory.¶Materials: Seven anaesthetised, paralysed and ventilated healthy pigs of 21 kg.¶Measurements: P/V curves up to a pressure of about 40 cmH₂O were recorded with a computer-controlled ventilator. P_st/V curves were obtained with the static occlusion method and P_dyn/V curves during an insufflation at a low, constant flow rate.¶Results: P_dyn/V recording showed a complex pattern. During the insufflation compliance increased, fell, increased and fell again. A 2nd ¶P_dyn/V recording immediately following the 1st one was displaced towards higher volumes and showed only one maximum of compliance. The difference between the two curves reflected: (1) lung collapse during a period of 5 min of ventilation at zero end-expiratory pressure (ZEEP) following a recruitment manoeuvre, (2) recruitment during the measurement of the 1st P_dyn/V curve. These observations were similar in the supine and in the left lateral position. After ventilation at PEEP, 4 cmH₂O, the signs of collapse and recruitment were reduced. It was confirmed that PEEP offers a partial protection against collapse. P_st/V curves showed higher volumes and higher compliance values compared to P_dyn/V curves. This reflects the influence of viscoelastance on P_dyn/V curves.¶Conclusion: The study demonstrates a particularly strong tendency to lung collapse in pigs.     

Factors limiting exercise performance in progressive systemic sclerosis

In order to evaluate to which extent various organs limit physical performance in PSS, maximal working capacity was studied in 22 patients. Special attention was given to cardiac and pulmonary function, joint mobility, and muscular strength. A model for scoring these parameters is given. Working capacity was on the average 51% of the predicted normal value. Ventilation at maximal workload was high despite normal arterial blood gases and presumably normal physiologic dead space. This can be explained by an increased demand on ventilation from an increased muscle metabolism. This may be due to impeded mobility of respiratory and locomotive organs.The maximal heart rate was low and patients with low physical capacity had only a small decrease in base excess. One third of the patients developed arrhythmia during exercise, which contributed to a low performance. Other myocardial involvement was common, seen in the Q-waves, low voltage, left axis deviation, and increased heart volume. In PSS, these ECG changes probably reflect myocardial fibrosis that has developed without clinically manifest infarction. Special attention must be given to arrhythmias at work, which are overlooked in a resting ECG. Ventricular tachycardia plays an important role in sudden death, which, when it occurs, almost always does so within the first years after the onset of PSS.There was no close linkage between cardiac dysfunction and pulmonary fibrosis or joint-muscle impairment. The scoring system showed an equal distribution in reduction of working capacity as to circulation, pulmonary function, and locomotive function. Irrespective of the degree of work reduction, at least two organ systems were impaired in almost all of the patients. This emphasizes the complexity of the disease which is already in its early stage.