Unintended consequences may emerge, however, especially due to potential increases in the inhalation of pollutants as the population walking or cycling in polluted environments increases.
The incidence of hepatocellular carcinomas that metastasized to the lungs was also significantly increased in the inhalation studies.
The first hypothesis is not in accordance with the lack of toxic effects on the bone marrow (a target organ of known leukemogenic compounds), the negligible increase in blood FA levels in inhalation studies, and the lack of leukemogenic effect in animal studies.
Positron emission tomography provides similar results: the reduction of cerebral blood flow and the increase in oxygen extraction during inhalation of 100% oxygen is completely reversed when subjects breathe carbogen (5% carbon dioxide, 95% oxygen) [ 27].
SQ-standardized HDM SCIT provided a statistically significantly higher HDM-allergen tolerance (P < 0.05 vs placebo) in terms of a 1.6-fold increase in PD20 (HDM-allergen inhalation challenge), a 60-fold increase in skin test histamine equivalent HDM-allergen concentrations, reduced immediate- and reduced or abolished late-phase skin reactions, as well as fewer patients with LAR.
In one study that showed a clear increase in sputum neutrophils after inhalation of 20,000 Endotoxin Units (i.e. 2 μg) [ 8], the baseline sputum induction was performed just prior to the LPS challenge, which could have enhanced the neutrophil response [ 19].
In addition, similar increases in testicular interstitial cell tumors in inhalation studies of ethylbenzene (NTP 1999a) and isoprene (NTP 1999b) in F344 rats were considered related to chemical exposures.
Recent research focusing on molecular mechanisms involved in inhalation injury has increased the number of potential therapies.
Previous results suggest that CBF increases by approx. 90% during inhalation of 6% CO2 (ΔpCO2 = 22 mmHg) (Reivich 1964; Grubb et al. 1974) or 50% increase in CBF for 5% CO2 inhalation (ΔpCO2 = 11 mmHg).
For tissue collection, animals were sacrificed using slow initiation of carbon dioxide inhalation, with increase in concentration gradually, for ∼1 min, followed by cervical dislocation.
