Hematopoietic stem cells (HSCs), which govern the production of all blood lineages, transition through a series of functional states characterized by expansion during fetal development, functional quiescence in adulthood, and decline upon aging.

Although research on aging has for a long time been relatively descriptive, much progress has been made in the past decade to uncover the molecular drivers of biological aging. One such drivers relates to stem cell exhaustion.

The amount and the function of HSCs decline in humans along aging. This decline is characterized by different changes such as signaling, epigenetic, cell surface markers etc. Various studies have been conducted to identify HSCs surface markers using flow cytometry.

Exposure to Hyperbaric Oxygen Therapy (HBOT) induce stem cells proliferation mobilization of stem progenitor cells (SPCs) in both animal and humans studies, and the number of SPCs remain elevated in blood over the course of 20 HBOT .

Additionally, Heyboer et al have found dose response curve between the HBOT protocol and circulating CD34+ and CD45-dim (stem cells potential markers): increasing the treatment pressure from 2.0 ATA to 2.5 ATA increased the concentration of circulating stem cells.

The aim of the current study is to evaluate the effect of HBOT on circulating hematopoietic stem cells, in the peripheral blood of patients who are candidate for HBOT.

Inclusion Criteria:

• The study will include patients aged 20-80 who are intendent to start HBOT for other indication that are willing to give blood samples for measurements of circulating stem cells.

Exclusion Criteria:

1. Active or recent infection within the last month
2. Active malignancy.
3. History of hematopoietic disease
4. Low B12 or iron levels
5. Inability to sign the informed consent form
6. Leucocytes ˂4000 or ˃10,000