Role of Arterial Pressure, Wall Stiffness, Pulse Pressure and Waveform in Arterial Wall Stress/Strain and Its Clinical Implications

Biomechanical stress applied to the intima of arteries has long been suspected as a factor in the initiation and localisation of atherosclerotic plaque, and it is implicated in the separation of plaque from the underlying arterial wall giving rise to the acute clinical consequences of thrombosis, dissection and embolism. The factors underlying transmural stress were investigated in-vitro using fresh porcine abdominal aortas on an experimental rig in which pulse pressure, pulse waveform, fluid viscosity, pulse rate, vessel wall compliance and systolic and diastolic blood pressure could be varied at will. Vessel wall compliance was progressively reduced by exposure of the artery to formaldehyde vapour for increased periods of time, a saline-treated artery being used as control. Centripetal transmural stress (CTS) and strain were studied by direct observation of the displacement of a compliant false intima (FI) using real-time B and M mode ultrasound, and by measuring the differential pressure between the space beneath the FI and the adjacent vessel lumen. CTS was found to be directly related to pulse pressure (r = 0.907, p < 0.001) and inversely related to vessel wall compliance. It was independently affected by ranked peak pressure waveform (R = 0.93, p < 0.01) being higher with sharp peak pressure and lower when the waveform was rounded, and it peaked in early diastole in untreated vessels, and both in diastole and peak systole in ones stiffened by formaldehyde vapour. Mean arterial pressure exerted a profound effect via its effect on vessel wall stiffness, which was found to rise 7-fold across the mean arterial pressure range 50-130 mmHg and continued to increase in a logarithmic fashion as the upper physiological range of mean arterial pressure was exceeded. There are two potential clinical implications: in mitigating the postulated biomechanical aspects atherogenesis and atherosclerotic plaque detachment, maintaining large vessel wall compliance is important, and the main factor determining this in a healthy artery is mean arterial pressure; if the arterial wall has already become stiffened as a result of disease, and in the absence of critical stenosis, the findings suggest that the appropriate therapeutic targets are modification of pulse pressure and pulse waveform profile. Simply reducing the diastolic pressure in elderly patients may be unwise if the result is a widened pulse pressure and increased transmural strain. The distribution of atheroma at points of focal mechanical strain in the vessel wall may be explicable if the stress induced by an excessive pulse pressure provokes the inflammatory changes seen in repetitive strain injury. Investigation of inflammatory signalling in the vessel wall provoked by repeated mechanical stress may represent a productive area for future research.

Gas-Particle Partitioning of Formaldehyde in Mainstream Cigarette Smoke

SummaryA diffusion denuder apparatus has been used to investigate the gas-particle partitioning of formaldehyde, acetaldehyde, acrolein and crotonaldehyde in cigarette mainstream smoke (MS), compounds that are of interest owing to their toxicity and near quantitative retention in the body during cigarette smoking. Formaldehyde showed the best performance in denuder experiments with simple aldehyde-air mixtures owing to the relatively fast rate of the heterogeneous reaction formaldehyde(g) + dinitrophenylhydrazine(s) → hydrazone(s). Analysis with the Gormley-Kennedy equation revealed that formaldehyde denuder removal approached, but did not attain, complete efficiency even under optimized operational conditions. Acetaldehyde, acrolein and crotonaldehyde were trapped with considerably lower efficiency than formaldehyde under the denuder conditions used, and more effective denuder wall coatings would be required to examine gas-particle partitioning of these other carbonyls. The proportion of formaldehyde in the smoke particulate phase initially entering the denuder was > 99%, but loss of formaldehyde from the smoke particles was relatively rapid leading to 35%–61% deposition over the denuder length. The temperature dependence of formaldehyde deposition in the denuder was well predicted using Henry's law constant for aqueous formaldehyde solutions. These observed properties of formaldehyde are primarily due to reversible reactions of formaldehyde with water in cigarette smoke leading to the much less volatile species methanediol, its oligomers and hydrate. These data suggest that cigarette smoke inhalation is likely to expose the deeper-lung generations of smokers to greater relative formaldehyde exposure, and greater genotoxic risk at those generations than might occur through inhalation of formaldehyde vapour alone.Risk assessments of formaldehyde in cigarette smoke should be updated to recognise this modified risk profile.

HISTOLOGICAL EFFECTS OF FORMALDEHYDE INHALATION ON THE ALVEOLAR ARCHITECTURE OF LUNGS OF ALBINO RATS

Introduction: Formaldehyde is a flammable, colourless, reactive, readily polymerized gas at normal room temperature and pressure. Formaldehyde vapour is readily absorbed from the lungs. Formaldehyde is combined with methanol and buffers to make embalming fluid. In the dissection hall, during embalming or cadaveric dissection and histo-pathological preservation, medical professionals are exposed to formaldehyde vapours. Respiratory system is the major target of formaldehyde. So, the present study aims to assess the histological changes on the architecture of alveoli of albino rats after inhalation of formaldehyde vapours. Material & Methods: 24 albino rats were exposed to formaldehyde vapours for 28 days. They were exposed with various concentrations and thus 4 groups, having 6 rats in each, were made. They were sacrificed and the lung tissue was taken and studied by using H & E stain. Results: The study shows a number of important histological changes which are concentration dependent. Conclusion: It may be concluded from the present study that concentration of formaldehyde can affect significantly on the histopathology of the lungs of albino rats.

Electrocardiographic interpretation of the nasopharyngealresponse in conscious rabbits

The present study was conducted to recognize by part, the cardiovascular events of the nasopharyngeal reflex, through electrocardiographic interpretations. ECG patterns were traced in twelve clinically normal and healthy New Zealand White rabbits of both sexes, weighing between 2-3 kg and aged between 1-3 years with inhalant irritants. Immediately after induction of formaldehyde vapour, the heart rate fell by 69% from a mean of 192 ± 7.310 bpm to 60 ± 1.296 bpm, whereas exposure with cigarette smoke caused a fall in heart rate by 74% from a mean of 205 ± 9.605 bpm to 53 ± 3.065 bpm. With both irritants, P wave becomes smaller and totally disappeared, indicating an increased vagal activity inducing a sinoatrial node arrest. The amplitude of QRS complex also significantly decreased; and so did the duration of P wave and PR interval, presumably due to junctional escape. T wave duration decreased with slow ventricular repolarization. Bradycardia was also evident with increased QT interval. However, there was no change in QRS complex or ventricular depolarization, mediated perhaps via compensatory sympathetic influence on the ventricular myocardium. The study demonstrates that both formaldehyde and cigarette smoke provoked a similar protective response of rabbits against noxious fumes.

Photocatalytic Oxidation of Formaldehyde Vapour Using Amorphous Titanium Dioxide

The gas-phase photocatalytic oxidation of formaldehyde over illuminated amorphous titanium dioxide was investigated using a model flow reactor with the following experimental conditions: 0.1–0.5 l/min flow rate and an organic compound concentration range of 0.006–0.082 mol/m3. Mathematical model of the process which includes two sequential stages: formation of formic acid and its subsequent oxidation to CO2 was offered. It was found that when the amount of TiO2 on carrying agent (anodized titanium) is 3.6 mg/cm2, the intensity of UV lamp is 18 W and the catalyst temperature is 293 K, values of observed rate constants are equal to 6.5.10−3 s−1 for the first stage and 1.10−2 s−1 for the second stage of oxidation. The apparent activation energy of photocatalytic oxidation process of formaldehyde vapour for temperature interval 293 – 323 K is 20.2 kJ/mol.