Microelectrodes for in-vivo determination of pH - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 258

10.5.4 Measurement of pH in the heart
10.5.5 Measurement of pH in the esophagus
10.5.6 Measurement of pH under skin
10.5.7 Measurement of pH in the eye
10.6 Conclusions and outlook
10.7 Acknowledgments
10.8 References
10.1 INTRODUCTION
pH measurement techniques have been widely used in chemical, biological, biomedi-
cal, and clinical laboratories. Reliable and accurate analytical methods are essential for
successful pH monitoring in vivo . The method should require only a small volume of
sample, and be rapid, simple, and reliable. Potentiometric measurement using microe-
lectrodes is the technique of choice for most in-vivo applications of pH determination.
10.1.1 Signifi cance of pH measurement in vivo
pH is a critical measurement for our human health. The monitoring of pH levels can
serve as a marker for diagnosing diseases, as a guide for optimizing medical treatments,
and as an indicator for monitoring biochemical and biological processes. When the
body's ability to regulate its pH is compromised, the consequences are serious. In cancer
research, an elevated intracellular pH is an important trigger for cell proliferation [1, 2].
Intracellular pH in tumor cells is normal or slightly alkaline; in contrast, extracellular
pH, which varies with the type of tumor, is usually acidic. Intracellular pH has been
shown to be alkaline in cancer cells [3]. Rich et al. [4] noted that the intracellular pH
was approximately 0.4 units higher in various leukemia cell lines and leukemia cells than
in peripheral blood mononuclear cells from healthy donors. The reduction of intracel-
lular pH resulted in inhibition of overexpression of cyclooxygenase-2 enzyme in human
colon cancer cells [5]. Measurement of extracellular pH can provide guidance not only
for cancer diagnosis but also for choice of therapy. Most chemotherapeutic agents are
weak bases or weak acids, so the measurement of pH gradient in cancer cells can help to
determine their therapeutic effi cacy [3].
Furthermore, pH determination has been used in other clinical research, both alone
and in combination with other measurements. This research includes studies into the
relationship between extracellular and intracellular pH in an ischemic heart [6, 7], the pH
of airway lining fl uid in respiratory disease [8], the study of pH as a marker for pyloric
stenosis [9], malnutrition in alkalotic peritoneal dialysis patients [10], pH modulation of
heterosexual HIV transmission [11, 12], and wound prevention and treatment [13]. In
addition, pH changes due to blood acidosis have been used to trigger and pace the ven-
tricular rate of an implanted cardiac pacemaker [14]. Research using pH measurements